Silent development of memory progenitor B cells.

T cell-dependent immune responses generate long-lived plasma cells and memory B cells, both of which express hypermutated Ab genes. The relationship between these cell types is not entirely understood. Both appear to emanate from the germinal center reaction, but it is unclear whether memory cells evolve while obligatorily generating plasma cells by siblings under all circumstances. In the experiments we report, plasma cell development was functionally segregated from memory cell development by a series of closely spaced injections of Ag delivered during the period of germinal center development. The injection series elevated serum Ab of low affinity, supporting the idea that a strong Ag signal drives plasma cell development. At the same time, the injection series produced a distinct population of affinity/specificity matured memory B cells that were functionally silent, as manifested by an absence of corresponding serum Ab. These cells could be driven by a final booster injection to develop into Ab-forming cells. This recall response required that a rest period precede the final booster injection, but a pause of only 4 days was sufficient. Our results support a model of memory B cell development in which extensive affinity/specificity maturation can take place within a B cell clone under some circumstances in which a concomitant generation of Ab-forming cells by siblings does not take place.

Presence of activated antigen-binding B cells during immunization enhances relative levels of IFN-gamma in T cell responses.

To examine the influence of Ag presentation by B cells on immune responses, we have used mice transgenic for an Ig heavy chain from a monoclonal anti-azobenzenearsonate (Ars) Ab to deliver Ag to B cells during immunization. A large proportion of transgene-expressing B cells in these mice binds Ars, while transgenic serum Ig shows poor Ars binding. Transgenic B cells present Ars proteins better than their nonhaptenated counterparts. This is associated with an increase in the proliferative responses of transgenic T cells to Ars protein immunization. Although B cell numbers in the transgenic mice are lower, many B cells in them show an activated phenotype, as identified by altered surface levels of peanut agglutinin reactivity, CD23, CD24, CD44, CD62L, and CD86. Even against nonhaptenated immunogens, transgenic responses show significant enhancement in the relative proportions of the Th1 cytokine IFN-gamma over the Th2 cytokines IL-4 and IL-10. Haptenated immunogens further enhance the predilection of transgenic mice to produce relatively more IFN-gamma. Consistent with this, there is an increase in IgG2a/IgG1 ratios in serum Abs in response to haptenated immunogens in transgenic mice. Adoptive transfer of primed hapten-specific secondary B cells into nontransgenic mice also induces an increase in relative levels of IFN-gamma in response to haptenated immunogens. Thus, presentation of immunogen in vivo by activated Ag-binding B cells contributes to enhanced immunogenicity and a Th1 cytokine bias.

Evaluation of the role of the 3'alpha heavy chain enhancer [3'alpha E(hs1,2)] in Vh gene somatic hypermutation.

Previous work on the cis-acting elements that control heavy chain variable region (VH) gene somatic hypermutation has indicated the presence of an as yet unidentified element(s) 3' of the intron enhancer that is necessary for high rate mutation. Examination of cis-acting elements involved in kappa light chain V gene hypermutation has demonstrated a requirement for both the intronic and 3' kappa enhancers in this process. To examine whether the 3'alpha heavy chain enhancer [3'alpha E(hs1,2)] is required for somatic hypermutation of VH genes, we generated two types of transgenic mice. One type was generated using a construct containing a VH promoter, a rearranged VDJ, the heavy chain intronic enhancer, and the murine heavy chain 3'alpha E(hs1,2). The transgenes in the second lines were similar to the transgenes in the first with the addition of a second complete matrix attachment region (MAR) 3' of the heavy chain intronic enhancer, and splice acceptor and polyadenylation sites between the two enhancers. Analysis of both transgenes revealed levels of mutation at least 10-fold lower than endogenous VH genes. These data suggest that the 3'alpha E(hs1,2) does not play a role analogous to the 3' kappa enhancer in the regulation of the hypermutation process. Moreover, in one of the transgenes, the presence of the 3'alpha E(hs1,2) resulted in a lack of transcription in vivo, suggesting a negative regulatory role for this enhancer in certain contexts.

Leukocyte-derived neutrophil chemotactic factor-2 produced by infiltrated leukocytes in allergic inflammation model in rats is macrophage inflammatory protein-2.

In the air pouch-type allergic inflammation model in rats, leukocytes collected from the pouch fluid 4 h after the antigen challenge produced proteinaceous chemotactic factors for neutrophils. The leukocytes from the immunized rats produced significantly higher amount of the chemotactic factors than that from the non-immunized rats. The major chemotactic factor, leukocyte-derived neutrophil chemotactic factor (LDNCF)-2, was purified and found to be identical with rat macrophage inflammatory protein (MIP)-2 by N-terminal amino acid sequence analysis. Expression of MIP-2 mRNA was higher in the leukocytes from the immunized rats than that from the non-immunized rats. Possible roles of LDNCF-2 (MIP-2) in neutrophil infiltration in the allergic inflammation is discussed.

Characterization of methylated bovine serum albumin-induced allergic inflammation in rats.

An air pouch type allergic inflammation in rats was induced using an insoluble cationic protein, methylated bovine serum albumin (MeBSA), as an antigen. Changes in vascular permeability, local tissue edema, histamine contents in the pouch fluid, and number of infiltrated leukocytes and chemotactic activity in the pouch fluid were analyzed during an 8-hour period after injecting the antigen solution into the air pouch of the immunized and nonimmunized rats. Vascular permeability during the first 30-min interval in the immunized rats was higher than that in the nonimmunized rats, reflecting a higher histamine level in the pouch fluid. However, both the increase in vascular permeability and histamine level in the immunized rats in this period were much lower than those induced by a soluble, noncationic antigen, azobenzenearsonate-conjugated acetyl bovine serum albumin. In the MeBSA-induced allergic inflammation model, a second peak of vascular permeability was induced at 2 h, and local tissue edema formation became apparent at 2 h, reaching a plateau at 4 h. A prominent increase in leukocyte infiltration, especially neutrophils, into the pouch fluid was induced at 4 h in accordance with an increase in chemotactic activity in the pouch fluid. These observations indicate that the acute phase of MeBSA-induced allergic inflammation is characterized by a weak anaphylactic response and a prominent neutrophil infiltration.

ABA-specific responses are I region restricted by the carriers used for immunization.

Immunization of mice with ABA coupled to carriers to which they are nonresponders gives rise to ABA-specific proliferative responses in lymph node cells. When C3H/HeN and CBA/J nonresponder mice are immunized with ABA on (T,G)-A-L (an I-A-restricted carrier in responder mice), the responses to ABA-tyr and ABA coupled to a variety of unrelated carriers are solely I-A restricted as determined by inhibition with anti-IA and anti-I-E sera. When ABA on GLT (an I-E-restricted carrier in responder mice) is used for immunization, the responses are both I-A and I-E restricted. Thus, ABA-specific responses in nonresponder mice appear in part to be restricted by the carrier used for immunization. B10.S mice, lacking functional I-E molecules, channel their ABA-specific responses entirely through I-A when immunized with ABA-GLT. These results support the hypothesis that the failure in nonresponders lies in a functional deficit in the T cell repertoire rather than an inability of accessory cells to present antigen.

Idiotypic analysis of polyclonal and monoclonal anti-p-azophenylarsonate antibodies of BALB/c mice expressing the major cross-reactive idiotype of the A/J strain.

The idiotypic cascade allows the induction of silent idiotypes, and as such, the immune system can be reprogrammed towards predetermined goals. To understand the genetic origin of silent idiotypes, we have used a system in which detailed structural and genetic information is available. The major cross-reactive idiotype (CRIA) of A/J mice (positive strain) immunized with arsonate coupled to a carrier can be regularly induced in BALB/c mice (negative strain) by anti-idiotypic treatment with or without subsequent antigen immunization. By using a panel of monoclonal anti-idiotypic antibodies, we have found that the germline-encoded CRIA displays a mosaic of at least five idiotopes. Polyclonal and monoclonal anti-arsonate antibodies prepared from idiotypically manipulated BALB/c mice have been studied. Four germline idiotopes are shared between the CRIA of the A/J strain and the CRIA-like idiotype induced in BALB/c mice. Furthermore, CRIA-like antibodies can appear "spontaneously" in some BALB/c mice immunized with antigen only. The data suggest that anti-idiotypic treatment in BALB/c mice selects a preexisting subset of antibodies. From the serological analysis, it is predicted that CRIA molecules from A/J and CRIA-like molecules from BALB/c employ different VH subgroups but share some components of the hypervariable regions. These predictions are tested in a forthcoming paper that describes the amino acid sequences of BALB/c monoclonal antibodies displaying the major cross-reactive idiotype of the A/J strain.

Expression and regulation of two idiotype families and subsets within an idiotype family among BALB/c antibodies against p-azophenylarsonate.

The expression and regulation of the two different idiotype (id) families associated with the anti-p-azophenylarsonate (Ar) antibodies of BALB/c mice were examined. Both families ( 5AF6 and 3C6 ) represented cross-reactive idiotypes (CRI) expressed in the anti-Ar of most individual BALB/c mice. In response to keyhole limpet hemocyanin-Ar, an average of about 28% of BALB/c anti-Ar had 5AF6 family idiotopes, while 3C6 family was expressed on about 16% of BALB/c anti-Ar antibodies. Suppression induced by anti-idiotype treatment against one family did not suppress the expression of the other family, suggesting that the two families were regulated independently. However, the relative expression of one family could influence the expression of the other, because depression of the 5AF6 family tended to increase the expression of the 3C6 family of anti-Ar. Analysis of the 5AF6 family showed that a majority of BALB/c mice produced antibodies bearing most or all of the idiotopes associated with the family, but that a subset of about 35% of the antibodies synthesized lacked idiotopes associated with a monoclonal anti-Ar member of this family, 2.4. Treatment of mice with anti-idiotypes prepared against two different monoclonal anti-Ar of the 5AF6 family produced different effects: one enhanced while the other suppressed idiotype expression, suggesting that there are differences in the idiotopes associated with these two regulatory pathways. Additionally, results indicated that subsets of antibodies within the 5AF6 idiotype family could be regulated independently of each other.

Depletion of murine anti-azobenzenearsonate plaque-forming cells by derivatized polyacrylamide beads.

The depletion of secondary p-azobenzenearsonate plaque-forming cells (ABA-PFC) by affinity columns substituted with ABA was dependent on the primary dose, times elapsed after priming, and the nature of the side-arm on the columns. Thus, higher priming doses of ABA coupled to keyhole limpet haemocyanin (50-500 micrograms of ABA-KLH in complete Freund's adjuvant (CFA] favoured depletion of ABA-PFC by ABA coupled to a 6- aminocaproyltyrosine side-arm (SAC-TYR-ABA beads), whereas ABA-PFC from mice primed with 1 microgram of ABA-KLH in CFA were never depleted; this latter population were only depleted by ABA coupled to a histamine side-arm (HIST-ABA beads) 7 months after priming. These data are consistent with the notion that two specificities, HIST-ABA and TYR-ABA, appear to emerge independently, lower priming doses inducing the preferential appearance of the HIST-ABA specificity.

Regulation of azophenylarsonate-specific repertoire expression. II. Fine specificity and isotype heterogeneity of anti-arsonate antibodies.

This report investigates the isotope and binding site heterogeneity of IgG anti-azophenylarsonate (ARS) monoclonal antibodies derived from splenic fragment cultures of nonimmune and immune A/J mice. By using five arsanilic acid derivatives in a hapten inhibition assay to determine fine specificity, the secondary ARS-specific repertoire was found to be extremely heterogeneous, with 52 unique patterns among the 81 antibodies analyzed. CRIA+ and CRIA+/- clonotypes were as heterogeneous as CRIA- antibodies, but a majority of CRIA+/- clones maintained a characteristic relative affinity for two of the haptens, p-arsanilic acid (p-ARS) and p-azobenene arsonic acid-N-tyrosine (ABA-tyr), which was identical to the prototype CRIA+ hybridoma protein R16.7. We also observed that the average relative affinity of CRIA- antibodies from immunized donors was higher than nonimmune mice with respect to p-ARS and ABA-tyr, and that there was a further increase in avidity to ABA-tyr over time after immunization. In contrast, no affinity maturation occurred among the CRIA+ and CRIA+/- clones. Rare antibodies were also identified within the nonimmune repertoire that had higher relative affinities than R16.7. Despite this, a greater proportion of CRIA+ and CRIA+/- clones produced IgG antibody in vitro. Thus, the predominance of CRIA+ antibodies in the ARS-specific immune repertoire and the preferential differentiation of CRIA+ precursor cells to IgG secretors cannot be entirely explained by the avidity of this clonotype family for p-ARS or ABA-tyr.

Antigen- and receptor-driven regulatory mechanisms. X. The induction and suppression of hapten-specific granulomas.

We have investigated the induction and suppression of granuloma formation elicited by the azobenzenearsonate (ABA) determinant in A/J Mice. ABA-derived syngeneic spleen cells (ABA-SC) administered subcutaneously induced hapten-specific delayed hypersensitivity (DTH), detected by footpad swelling, upon challenge with ABA-bovine serum albumin (BSA) coupled to polyacrylamide beads (PAB). The reactions elicited by ABA-BSA-PAB reached maximal intensity at 24 hours but were relatively persistent and were still marked at 96 hours. Histopathologic examination of footpad responses at 24 and 48 hours after challenge revealed compact collections around beads of mononuclear cells and granulocytes, which were characteristic of DTH reactions. Discrete epithelioid granulomas became apparent by 72 or 96 hours. Unprimed mice or mice primed with ABA-SC and challenged with uncoupled beads did not develop either substantial leukocytic infiltrates or granulomas. Persistent delayed responses were only apparent if the mice were challenged with the homologous hapten-coupled bead, indicating the fine specificity of the reaction. Immune cells were shown to be capable of transferring DTH and granulomatous responsiveness to ABA; the cells were sensitive to anti-Thy 1.2 antiserum and complement, which indicates that the response was thymic-dependent. The intravenous injection of ABA-SC, which is known to induce suppressor cells, prevented the development of DTH or granulomatous responsiveness followinggg subcutaneous immunization with ABA-SC. In addition, the transfer of suspensions containing suppressor T cells into syngeneic mice primed with ABA-SC prevented the development of DTH reactions and granuloma formation followin challenge with ABA-BSA-PAB. Furthermore, only hapten-specific suppressor T cells limited persistent delayed hypersensitivity responses. Having successfully developed granulomas in the footpad, the authors induced and suppressed granulomatous lesions in the gastrointestinal tract in a similar fashion. These experiments establish a model in inbred mice for the study of granulomatous diseases, including those of the gastrointestinal tract.