Effects of IL-4 depletion on the antibody response to Pseudomonas aeruginosa lipopolysaccharide in mice.

These studies were done to examine the role of interleukin-4 (IL-4) in the generation of isotype specific antibody responses of mice to Pseudomonas aeruginosa lipopolysaccharide (PALPS) by neutralization of IL-4 in vivo using anti-IL-4 antibody (11B11). We found that the administration of anti-IL-4 antibody (11B11) 24 h before immunization with PALPS resulted in a decreased PALPS-specific antibody response for all isotypes examined (IgM, IgG1, IgG2a, IgG2b, IgG3). By contrast, we observed that the non-antigen-specific (polyclonal) IgM response of mice following treatment with 11B11 antibody and PALPS was increased while the polyclonal responses for the other isotypes were unaffected. When mice were given recombinant IL-10 at the time of immunization with PALPS there was a decrease in the PALPS-specific antibody response but an increase in the polyclonal IgM, IgG2a, IgG2b, IgG3 response whereas the polyclonal IgG1 response was decreased by a five-fold margin. The results of these studies suggest that both the antigen-specific and the polyclonal response can be influenced in a different manner by IL-4 or by IL-10.

Induction of differentiation in a B lymphoma X B lymphocyte hybrid line. II. Intraclonal heterogeneity in growth, secretion of IgM, and cytokine production in response to lipopolysaccharide.

Murine B lymphocyte clones have proven to be useful models to study aspects of B lymphocyte growth and development. It had been previously shown that induction of TH2.2 (B lymphoma X B lymphocyte) with LPS resulted in differentiation into IgM-secreting cells (a feature similar to other B cells lines such as BCL1), and secretion of granulocyte-macrophage-CSF. Many transformed and nontransformed lines (including TH2.2) have been shown to generate progeny heterogenous in size and secretion of product when exposed to mitogen. We extend this study to demonstrate heterogeneity in secretion of IgM, granulocyte-macrophage-CSF, IL-3, and IL-6 in LPS-induced TH2.2. Clones generated by limiting dilution were heterogenous with respect to size, type, and quantity of product secreted. Microscopic clones ranged from 10 to about 1000 cells in size and could not be grown further; the majority secreted one product (mainly IgM). These clones were very efficient secretors of IgM and probably consist mainly of terminal-secreting cells. Microscopic clones secreting cytokine were also efficient producers. Visible clones from LPS-induced cultures grew to the same size as uninduced clones and were often restricted in secretion of products. Although the majority secreted three of four products (52%), many secreted IgM only or IgM and one cytokine. Although there was a strong tendency for clones to secrete multiple products, almost every secretory phenotype could be found. Amounts of different products secreted were not correlated, suggesting an additional level of independent control of this variable. Restriction of secretion was not due to genetic variation because visible clones originally restricted in secretion almost always produced all products when expanded and retested. These findings indicate that cells of TH2.2 were heterogeneous with respect to growth and secretion in the presence of LPS and were individually programmed for differentiative responses. The programming of cells was not permanent, but subject to dynamic change.

Augmented IgG anti-acetylcholine receptor response following chronic penicillamine administration.

A model of D-penicillamine (DP) induced myasthenia gravis (MG) was developed in which the anti-acetylcholine receptor (anti-AChR) antibody response to AChR challenge was increased in mice chronically treated with DP. To investigate the mechanism of the DP induced increase, IgM and IgG anti-AChR responses to AChR challenge were studied. IgG responses were significantly greater in the DP treated mice than in the control group while IgM responses were not significantly different. This change appeared to be relatively specific for the AChR response because neither serum immunoglobulin levels nor the IgG response to a second antigen (purified protein derivative) were increased by DP treatment. These results suggest that a specific sensitization to AChR occurs during chronic DP treatment.

A VIP antagonist distinguishes VIP receptors on spinal cord cells and lymphocytes.

Vasoactive intestinal peptide (VIP) is a neuropeptide which also interacts with cells of the immune system. The paucity of specific VIP receptor antagonists has hampered studies of possible receptor heterogeneity and of VIP function. To aid in achieving these goals, a new VIP antagonist, a hybrid between neurotensin and VIP, has been synthesized. This peptide interacted with VIP receptors on spinal cord cells with an affinity 10-fold greater than VIP itself. In contrast, 1000-fold higher concentrations of the antagonist were required to displace labeled VIP from its receptor on lymphoid cells as compared to VIP itself, suggesting VIP receptor heterogeneity between immune and spinal cord cells.

Nonspecific and Candida-specific immune responses in mice suppressed by chronic administration of anti-mu.

CBA/J mice were immunosuppressed by repeated administration of goat antibody specific for mu chain of immunoglobulin M (IgM) and tested for nonspecific and Candida albicans-specific immune responses. Immunosuppression was demonstrated by a dramatic reduction in the number of antibody-forming cells in the spleens of anti-mu-treated mice when immunized with sheep erythrocytes, by greatly reduced in vitro responsiveness of both spleen and lymph node lymphocytes from anti-mu-treated mice to lipopolysaccharide, and by a large reduction in the number of splenic IgM-positive cells. T cell function, on the other hand, appeared to be relatively unaltered in anti-mu-treated animals, in the cytotoxic T lymphocyte activity against an allogeneic target was similar in splenocyte cultures from anti-mu- and mock-treated animals, and splenic and lymph node lymphocytes proliferated in response to concanavalin A in a lymphocyte stimulation assay. Moreover, Candida-specific delayed hypersensitivity to two different Candida antigens, one cell wall-derived (GP) and the other cell membrane-derived (BEX), was of comparable intensity in immunosuppressed and normal animals. When anti-mu- and mock-treated mice were immunized by the cutaneous inoculation of viable C. albicans blastospores and then challenged intravenously to assess the development of protective immunity, only mock-treated animals, male and female, had significant (p less than or equal to 0.05) protective responses demonstrable by reduction in the number of colony-forming units cultured from their kidneys 28 days after intravenous challenge. If consideration was given to the number of animals which had cleared Candida completely from the kidney, however, there appeared to be protective responses operative in the female anti-mu-treated animals as well. Neither anti-mu-treated males nor females, when immunized and challenged with C. albicans, produced Candida-specific antibody detectable by counterimmunoelectrophoresis, whereas all immunized and challenged mock-treated animals produced antibody. The data are consistent with the hypothesis that anti-mu treatment has little effect on multiple cellular immune functions, including those specific for C. albicans, and the combination of antibody, cell-mediated immunity and innate defenses are responsible for solid systemic defense against the fungus.

Inbred mice infected with Plasmodium yoelii differ in their antimalarial immunoglobulin isotype response.

Antibodies are known to be important in mediating malarial immunity, but the influence of the various immunoglobulin isotypes on parasite elimination is unclear. The purpose of this study was to provide basic information on the induction of isotype expression in genetically different mice during primary malaria. Parasitaemias and the serum antimalarial IgM, IgG1, IgG2, IgG3 and IgA antibody titres measured in a radioimmunoassay were followed in outbred and 11 inbred strains of mice infected with 17XNL Plasmodium yoelii. Severity of infection, as judged by length of infection, peak parasitaemias and death, was found to differ between the strains. All strains developed rapid IgM responses, but only 3/11 inbred strains produced significant antimalarial IgG1 levels during primary infection. All strains produced an IgG2 response, which developed slightly more quickly in strains with the least severe courses of malaria. A large variation in the IgG3 response was noted between strains. In general, IgG3 antibodies were the first IgG-isotype to appear in serum. They were detected as early as day 8 in strains that developed mild infections but were not present until around day 20 in strains with the most severe cases of malaria. Only one strain produced detectable antimalarial IgA antibodies. These results show that different patterns of isotype expression are induced in inbred strains of mice during primary P. yoelii infection.

Induction of granulocyte-macrophage colony-stimulating factor by lipopolysaccharide and anti-immunoglobulin M-stimulated murine B cell lines.

The present study was undertaken to elucidate whether B cell lymphoma and hybridoma cell lines can be stimulated by lipopolysaccharides (LPS) or by antibodies against immunoglobulin M (IgM) to produce granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF activity was assayed on the basophil/mast cell line PT-18 which is GM-CSF- and interleukin 3-dependent. Antibodies against murine recombinant GM-CSF were used to identify the colony-stimulating factor activity present in the supernatants of the stimulated B cell lines. When these cell lines were stimulated with LPS, two of five lymphoma and five of six hybridoma lines produced GM-CSF. Two cell lines, the B cell lymphoma M12.4.1 and the hybridoma TH2.2, were analyzed more extensively under serum-free conditions. In these two cell lines, the production of GM-CSF was dependent on the dose of LPS used and time of exposure. Antibodies against IgM stimulated the TH2.2 (IgM+) but not the M12.4.1 (IgM-) cells to produce GM-CSF. Northern blot analysis of the M12.4.1 and TH2.2 cells showed that mRNA of GM-CSF can be detected in LPS-stimulated but not in unstimulated cells. Our data show that transformed B cells can be stimulated to produce GM-CSF. The present data and previous studies on GM-CSF production by normal bone marrow-derived B cells suggest a possible participation of B cells in granulopoiesis.

Influence of Plasmodium chabaudi adami on the isotypic distribution of the antibody response of mice to sheep erythrocytes.

The influence of an infection with P. chabaudi adami on the isotypic distribution of the in vivo antibody response to SRBC was investigated. Previous experiments suggested that the IgG1 isotype was poorly represented in the antibody response to plasmodial antigens and in the non-specific B cell response which accompanies an infection with P. chabaudi. The experiments described here indicated that although the magnitude of the total primary or secondary in vivo PFC response to SRBC was relatively unaffected by infection, the SRBC-specific IgG1 PFC response was depressed. Maximum depression of the IgG1 component of the response was observed when the priming dose of SRBC was administered at the same time as or after infection with P. chabaudi organisms. Coincident with the depression in the IgG1 response in infected mice was a corresponding increase in the SRBC-specific IgM response. The IgG1 depression was not a consequence of different kinetics of the generation of an IgG1 response, since at all times measured, the IgG1-PFC response was lower. In addition, the depressed IgG1 responses occurred only during a viable infection and could not be induced by inoculation of large amounts of irradiated erythrocytic stages of the parasite. These data suggest therefore, that there is a selective depression of IgG1 antibodies (but not those of other isotypes) regardless of antigenic specificity as a result of infection of C57BL/6 mice with P. chabaudi adami.

Transfer of autoimmune encephalomyelitis with T lymphocytes in strain 13 guinea pigs.

Experimental autoimmune encephalomyelitis (EAE) and/or tuberculin sensitivity were transferred to histocompatible recipients with myelin basic protein-stimulated and/or PPD stimulated guinea pig lymph node T cells previously separated by depletion of B cells ("panning") on rabbit anti-guinea pig Ig antibody-coated Petri plates. The depletion was augmented by complement-mediated lysis using mouse anti-guinea pig B-cell monoclonal antibody (31D2), rabbit anti-mouse Ig, and rabbit complement. B cells did not transfer EAE nor provide protection against active immunization with guinea pig spinal cord antigen.

Protection and recovery in influenza virus-infected mice immunosuppressed with anti-IgM.

BALB/c mice, immunosuppressed from birth with goat anti-mouse IgM, were able to recover from influenza virus infection in the absence of detectable serum and nasal antibody. Recovery was delayed a few days when compared with control animals. Antibody-deficient mice, that had recovered from an initial influenza virus infection, i.e., convalescent mice, were subsequently rechallenged with homologous influenza virus in order to study the importance of nasal and serum antibody in prevention of infection. Convalescent mice were susceptible to reinfection when nasal and serum antibody were not detectable. The mice were resistant to reinfection when serum and/or nasal antibody was detectable by radioimmunoassay. Normal mice that were passively immunized with high titer mouse anti-influenza virus serum were susceptible to challenge with homologous influenza virus. The serum antibody levels in these mice were higher than most of those found in the immune convalescent mice suppressed with anti-IgM, thereby suggesting that the serum antibody, found in convalescent suppressed mice, is not protective. We conclude that 1) mice can recover from influenza virus infection in the absence of detectable levels of nasal and serum antibody, thus indirectly confirming the role of cell-mediated immunity in recovery; 2) serum IgM, IgG2A, IgG2B, IgG3, and probably IgG1 antibody levels are not responsible for protection against influenza virus infection of the upper respiratory tract; and 3) nasal IgA antibody correlates best with protection against reinfection of the upper respiratory tract, but some other locally protective agent cannot be excluded.

Distribution of immunoglobulin isotypes in the nonspecific B-cell response induced by infection with Plasmodium chabaudi adami and Plasmodium yoelii.

The nonspecific B-cell response induced by infecting mice with two nonlethal malaria parasites, Plasmodium chabaudi adami and Plasmodium yoelii, was analyzed in an isotype-specific reverse plaque assay. Our results showed different isotypic patterns in the two infections, although cells secreting immunoglobulin of all isotypes were increased to some extent. P. yoelii induced large increases in secreting cells of all isotypes; IgG2a-secreting cells were increased out of proportion to those of the other IgG classes. P. chabaudi induced large increases in secreting cells of all isotypes except IgG1. In addition, there was not a disproportionate increase in cells secreting IgG2a. The data show that these "polyclonal" responses are different during each infection. There are marked similarities between the distribution of "nonspecific isotypes" and the specific antibodies formed in each infection.

Immunoglobulin isotype distribution of malaria-specific antibodies produced during infection with Plasmodium chabaudi adami and Plasmodium yoelii.

The antibody response of mice to Plasmodium chabaudi adami and Plasmodium yoelii has been compared using a solid phase isotype-specific radioimmunoassay and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Serological cross-reactivity between these parasites was substantial. Studies using a radioimmunoassay detecting all classes of malaria-specific antibody demonstrated that during the early part of infection it was not possible to distinguish between homologous and heterologous reactions. Immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that 50% or more of the protein antigens detected were apparently shared by both parasites although the intensity of bands was always greater with homologous reactions. However, the distribution of isotypes in the antibody (Ab) response differed in the two infections. P. chabaudi infections were characterized by a predominant and persistent IgM response, moderate IgG2 and IgG3 and little significant IgG1 response during a primary infection. By contrast, IgM antibodies were transient in P. yoelii infection, IgG2 was the predominant isotype, and both IgG1 and IgG3 antibodies were present during a primary infection. These differences in isotypes were also detected when sera were tested on the heterologous antigen extracts suggesting that antigens shared by P. chabaudi and P. yoelii do not necessarily induce similar antibody responses in the two infections.

Augmented anti-acetylcholine receptor response following long-term penicillamine administration.

Because of the association of D-penicillamine (DP) therapy with myasthenia gravis, we have studied long-term DP treatment in five inbred strains of mice with doses comparable to those used in patients with rheumatoid arthritis. No clinical weakness or anti-acetylcholine receptor (AChR) antibody developed with up to 6 months of treatment, but augmented responses did occur to challenge with purified AChR in adjuvant. Anti-AChR antibody titers in C57BL/6 and C3H/He mice were significantly higher after challenge with AChR in DP-treated than in control mice. Augmented anti-AChR titers were not seen in strain A mice, but after 6 months of DP treatment increased susceptibility developed to the induction of experimental autoimmune myasthenia gravis. Nine weeks after challenge with purified AChR, 10 of 11 mice developed clinical weakness, leading to death in 6. Results of edrophonium testing were positive in 5 of 6 mice, and electrophysiological abnormalities were demonstrated in 3 of the surviving mice. Long-term DP treatment is associated with augmented anti-AChR antibody responses in C3H/He and C57BL/6 mice, and increased susceptibility to experimental autoimmune myasthenia gravis in strain A mice.

Effects of deoxycoformycin in mice. II. Differences between the drug sensitivities and purine metabolizing enzymes of transplantable lymphomas of varying immunologic phenotypes.

Transplantable BALB/c and AKR lymphomas of different cell surface immunologic phenotypes have distinctive patterns of response to the ADA inhibitor DCF in vivo and in vitro. BAL 9, a lymphoma of the Lyt-1+,2+ T cell phenotype, was the most sensitive to DCF in vivo, and its DNA synthesis was inhibited more than 95% when cultured in the presence of dAr and DCF in vitro. This was correlated with a 10-fold increase in dATP content. The ADA and AMPDA activities were both high. Two lymphomas of the Lyt-1-,2+ T cell phenotype, BAL 5 and AKTB - lt , as well as two B cell phenotype lymphomas, A20 .3 and AKTB -lb, were all moderately inhibited in their in vivo growth if enough DCF was administered. However, their DNA synthesis in vitro was only inhibited 8 to 24% by dAr and DCF, there was only a twofold increase in the accumulation of dATP, and ADA and AMPDA activities were both low in the two BALB/c lymphomas tested. BAL 13, the only lymphoma of the Lyt-1+,2- phenotype examined, was completely resistant to DCF in vivo and in vitro. When cultured in the presence of dAr and DCF there was a transient increase in dATP content, followed by an abrupt decline. AMPDA activity was five to seven times greater than in the other lymphomas tested. ADA activity was moderate. The activities of 5' nucleotidase and of adenosine kinase were low and approximately equal in all the BALB/c lymphomas. These results suggest that the response to DCF by lymphomas of various immunologic phenotypes can be correlated with their nucleoside metabolism. The sensitivity of BAL 9 and the resistance of BAL 13 to DCF are correlated with their tendency to accumulate dATP and with their AMPDA and ADA activity ratios. The moderate sensitivity to DCF in vivo of the other T and B cell lymphomas, however, could not be clearly explained by any of the in vitro parameters thus far investigated, and this suggests that mechanisms inhibiting lymphoma proliferation other than dATP accumulation may be operating.

The abnormal function of T cells in chronically anti-mu-treated mice with no mature B lymphocytes.

T cells from anti-mu-treated mice, normal goat serum ( NGS )-treated mice or untreated control mice were compared with respect to their surface antigenic phenotypes, T cell mitogenic responses, helper function and precursor frequency of helper T cells. Anti-mu treatment arrested the development of B cells at an immature stage, as determined by flow microfluorometry; it resulted in no serum IgM, but detectable levels of IgG by solid-phase radioimmunoassay. Proliferative responses to phytohemagglutinin and concanavalin A were significantly decreased in T cells obtained from mu-suppressed C57BL/6 mice, but not from control mice. When T cells from anti-mu-treated mice were tested in vitro for their helper activity to collaborate with B cells from nu/nu C57BL/6 mice to give plaque-forming cells to sheep red blood cells, they provided far less help than did T cells from control mice. The frequency of T helper cells, as measured by limiting dilution analysis, was much lower in the anti-mu- than in the NGS -treated mice. Cell mixing experiments provided evidence for active suppression of T helper function among splenocytes taken from mu-suppressed mice.

Cutaneous leishmaniasis in anti-IgM-treated mice: enhanced resistance due to functional depletion of a B cell-dependent T cell involved in the suppressor pathway.

The contribution of B cells and antibodies to either the resistance or susceptibility to cutaneous leishmaniasis has been investigated in mouse strains rendered B cell-deficient by treatment with anti-mouse IgM antisera from birth (mu-suppressed). These studies confirm that immunity to cutaneous disease in a normally resistant mouse strain (C3H/HeJ) is independent of antibody, but that B cells and/or antibodies are required for the evolution of suppressed DTH and the consequent disease susceptibility of BALB/c mice. Anti-IgM-treated BALB/c mice, which lacked detectable anti-leishmanial antibodies during the course of infection, displayed a sustained DTH response to leishmanial antigen and were able to control their cutaneous lesions. The enhanced resistance of mu-suppressed mice could be completely abrogated by transfer of suppressor T cells from infected control animals into mu-suppressed mice before their infection. Thus the suppressor T cells, which are generated during leishmanial infection in BALB/c mice, can effect suppression in the absence of antibody. Evidence that B cells or antibodies are required for the generation of suppressor T cells was demonstrated by using BALB/c mice in which suppressor T cells fail to be generated during infection as a result of prior sublethal irradiation. Splenic T cells from normal mice could overcome the resistance conferred by sublethal irradiation, whereas splenic T cells from mu-suppressed mice could not. Thus the enhanced resistance of mu-suppressed BALB/c mice appears to be a consequence of their lack of functional expression of a B cell-dependent T cell critical to the suppressor pathway.

Regulation of anti-hapten antibody responses in vivo: memory, carrier-specific Lyt-2+ T cells can terminate antibody production without altering the peak of response.

By using the classical hapten-carrier antigenic system (dinitrophenyl-keyhole limpet hemocyanin) (DNP-KLH), and positive immunoselective techniques for purification of lymphocyte subsets, we studied the kinetics and role of KLH-primed T cells in the termination of a secondary in vivo plaque-forming cell (PFC) response against DNP in the mouse. Separation of T cells by Lyt-2 phenotype and recombination of T cell subsets demonstrated that a single injection of KLH in complete Freund's adjuvant (CFA) concomitantly generated both helper and suppressor T cells in the spleens of primed mice. When these KLH-primed, purified T cells were transferred into irradiated recipients along with DNP-primed, purified B cells and DNP-KLH, helper activity was demonstrable first, with the early production of a high anti-DNP PFC response. Suppression of the PFC response was observed only after the response had fully developed; the PFC response was then "terminated" within a few days. Helper activity was obtained with the carrier-primed Lyt-2- T cell population, whereas suppression required the addition of Lyt-2+ T cells. Both activities were generated over a wide dose range, were specific for the priming antigen KLH, and could be detected as early as 8 days or as late as 9 mo after a single priming injection of KLH. Lyt-2+ T cells from unprimed donors or from animals primed with a different carrier did not have the capacity to terminate the response when added with the primed Lyt-2- helper T cells. Thus, we have now demonstrated the existence of carrier-specific, long-lived, "memory" suppressor T cells, which are initially generated in parallel with specific helper T cells. Whereas these memory suppressor T cells do not inhibit the induction of a secondary antibody response, they can effectively terminate it once it has developed, and may therefore account for the normal termination of antibody responses.

Functional studies on B-cell hybridomas with B-cell surface antigens. III. Differentiative response to phorbol esters.

Phorbol esters have been shown to induce differentiation of human lymphoid cells into the mature stage. Murine lymphocytes, however, have not been found to be induced the terminal differentiation by these products. In this study, TH2.52, a subclone of B-cell hybridomas between M12.4.1 B lymphoma of BALB/c mice and normal B cells of C57BL/6 (B6) mice was treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) and the differentiative effect of TPA was examined. TPA treatment inhibited the spontaneous proliferation of TH2.52 and induced significant IgM secretion by the hybrid. In contrast, M12.4.1 did not develop any IgM secretion when treated with TPA. The differentiative effect of phorbol esters on TH2.52 closely correlated with their tumor-promoting activity. In addition, the differentiative response of TH2.52 to TPA was completely blocked by retinoic acid (RA). Moreover, TH2.52 cells treated with TPA were demonstrated to decrease the expression of Iab, Iad molecules as well as IgM molecules on the cell membrane by analyses of flow microfluorometry (FMF) and quantitative absorption tests. On the other hand, Iad expression of M12.4.1 did not change under the same conditions. The result clearly demonstrates that TH2.52 cells can be induced to differentiate into IgM-secreting cells after treatment with TPA, followed by the decrease in the expression of B-cell surface antigens on the cell membrane.

Functional studies on B cell hybridomas with B cell surface antigens. IV. Direct effects of cytochalasin B on differentiation.

We previously established B cell hybridomas between M12.4.1 B lymphoma of BALB/c mice and normal B cell of C57BL/6 (B6) mice. These hybridomas express Iab, Iad, and IgM molecules on the cell membrane, and can induce the generation of IgM secretion when treated with purified goat anti-mouse-mu antibody (anti-mu) without T cell factors. In this study, TH2.54, a subclone of a B cell hybridoma, was treated with cytochalasin B (CB), a fungal product that disrupts microfilaments, and the direct effect of CB on the proliferation and differentiation of TH2.54 was examined. CB considerably suppressed the spontaneous proliferation of hybrid cells. This product, however, did not inhibit the generation of IgM secretion by TH2.54 treated with anti-mu. Surprisingly, CB could directly induce the development of IgM-secreting cells by TH2.54 at a relatively high frequency. Among cytochalasins, dihydrocytochalasin B (H2CB), cytochalasin C (CC), and cytochalasin D (CD) showed marked effects on the induction of IgM secretion as well as CB. In addition, the differentiative effect of CB was greatly inhibited by N6, O2-dibutyryladenosine 3':5'-cyclic monophosphate (dbc-AMP), but not by N2, O2-dibutyrylguanosine 3':5'-cyclic monophosphate (dbc-GMP). Analysis by flow microfluorometry (FMF), cytotoxicity assays, and quantitative absorption tests demonstrated that CB treatment of TH2.54 resulted in a significant decrease in the expression of Iab, Iad, and IgM molecules on the cell membrane. In contrast, parental M12.4.1 neither generated any IgM secretion nor changed Iad expression on the cell membrane under the same conditions. The present study suggests very strongly that microfilament-microtubule systems are not involved in the differentiative process of TH2.54 induced by anti-mu. The results also indicate that CB can provide the initiative signal for differentiation of TH2.54 into the maturation lineage; this is followed by a significant change in the expression of Ia and IgM molecules on the cell membrane.

Functional studies on B cell hybridomas with B cell surface antigens. II. Ia molecules on the cell membrane and the differentiative response to anti-mu antibody.

TH 2.52, a subline of the B cell hybridoma with Iab, Iad, and IgM molecules on the cell membrane, was treated with F(ab')2 fragments of purified goat anti-mouse mu antibody (anti-mu), and the change in the expression of surface Ia molecules was determined by microcytotoxicity assays, quantitative absorption tests, and analyses of flow microfluorometery (FMF). We have previously reported that TH 2.52 cells can markedly generate IgM after stimulation with anti-mu without T cell factors. In the present studies, it was shown that the expression of surface Iab molecules on TH 2.52, originated from normal B cells of C57BL/6 (B6) mice, significantly decreased after treatment with anti-mu. In contrast, Iad molecules derived from M12.4.1 lymphomas did not change under the same conditions. These results indicate that cross-linking of anti-mu with surface IgM molecules on TH 2.52 provides signals for differentiation into IgM-secreting cells; this is followed by a decrease in the expression of Iab molecules on the cell membrane. Furthermore, monoclonal anti-Ia antibody (anti-Ia) did not inhibit the generation of IgM-secreting cells by TH 2.52 cells treated with anti-mu. In addition, la- sublines of TH 2.52 obtained after mutagenesis with ethyl methanesulfonate (EMS), as well as the original TH2.52, could differentiate into IgM-secreting cells in the presence of anti-mu. These findings suggest very strongly that la molecules on the cell membrane are not required for the induction of IgM secretion by B cells treated with anti-mu.