B-1a transitional cells are phenotypically distinct and are lacking in mice deficient in IκBNS.

B-1 cells mediate early protection against infection by responding to T cell-independent (TI) antigens found on the surface of various pathogens. Mice with impaired expression of the atypical IκB protein IκBNS have markedly reduced frequencies of B-1 cells. We used a mouse strain with dysfunctional IκBNS derived from an N-ethyl-N-nitrosourea (ENU) screen, named bumble, to investigate the point in the development of B-1 cells where IκBNS is required. The presence of wild-type (wt) peritoneal cells in mixed wt/bumble chimeras did not rescue the development of bumble B-1 cells, but wt peritoneal cells transferred to bumble mice restored natural IgM levels and response to TI antigens. The bumble and wt mice displayed similar levels of fetal liver B-1 progenitors and splenic neonatal transitional B (TrB) cells, both of which were previously shown to give rise to B-1 cells. Interestingly, we found that a subset of wt neonatal TrB cells expressed common B-1a markers (TrB-1a) and that this cell population was absent in the bumble neonatal spleen. Sorted TrB-1a (CD93(+)IgM(+)CD5(+)) cells exclusively generated B-1a cells when adoptively transferred, whereas sorted CD93(+)IgM(+)CD5(-) cells gave rise to B-2 cells and, to a lesser extent, B-1b and B-1a cells. This study identifies a phenotypically distinct splenic population of TrB-1a cells and establishes that the development of B-1a cells is blocked before this stage in the absence of IκBNS.

Lentiviral-mediated gene therapy leads to improvement of B-cell functionality in a murine model of Wiskott-Aldrich syndrome.

BACKGROUND: Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency characterized by thrombocytopenia, eczema, infections, autoimmunity, and lymphomas. Transplantation of hematopoietic stem cells from HLA-identical donors is curative, but it is not available to all patients. We have developed a gene therapy (GT) approach for WAS by using a lentiviral vector encoding for human WAS promoter/cDNA (w1.6W) and demonstrated its preclinical efficacy and safety. OBJECTIVE: To evaluate B-cell reconstitution and correction of B-cell phenotype in GT-treated mice. METHODS: We transplanted Was(-/-) mice sublethally irradiated (700 rads) with lineage marker-depleted bone marrow wild-type cells, Was(-/-) cells untransduced or transduced with the w1.6W lentiviral vector and analyzed B-cell reconstitution in bone marrow, spleen, and peritoneum. RESULTS: Here we show that WAS protein(+) B cells were present in central and peripheral B-cell compartments from GT-treated mice and displayed the strongest selective advantage in the splenic marginal zone and peritoneal B1 cell subsets. After GT, splenic architecture was improved and B-cell functions were restored, as demonstrated by the improved antibody response to pneumococcal antigens and the reduction of serum IgG autoantibodies. CONCLUSION: WAS GT leads to improvement of B-cell functions, even in the presence of a mixed chimerism, further validating the clinical application of the w1.6W lentiviral vector.

Regulation of T-cell-independent and T-cell-dependent antibody production by circadian rhythm and melatonin.

Melatonin is a hormone that has immunomodulatory activity and is believed to influence the production of antibodies in mammals. The aim of the present study was to investigate the effect of suppressed melatonin synthesis on the antibody production. BALB/c mice were immunized with T-cell-dependent (TD) and T-cell-independent (TI) antigens and kept under (i) normal lighting, (ii) constant exposure to light, (iii) exposed to light and treated daily with melatonin. It was revealed that melatonin modulated TD and TI antibody production. Suppressed melatonin synthesis increased the amount of IgM, IgG1, IgG2b and IgG3 antibodies after immunization with TI antigen. The level of TD antibodies IgM, IgG2a, IgG2b and IgG3 also increased, however, the antigen-specific antibodies of IgG1 isotype significantly decreased in mice exposed to light. Daily melatonin treatment brought the antibody level back to normal. The antibody concentration in the sera of mice kept at normal lighting was significantly higher when the immunizations were performed in the evening. The action of melatonin on B cells via MT2 receptor was shown in vitro and in vivo.

Antibody response of immunodeficient (xid) CBA/N mice to Escherichia coli 0113 lipopolysaccharide, a thymus-independent antigen.

CBA/N mice, which possess an X-linked immunodeficiency (xid), produce a convincing antibody response to lipopolysaccharide derived from Escherichia coli 0113 (LPS 0113), a thymus-independent antigen. The antibody response produced was shown to be specific for the O-polysaccharide moiety of LPS 0113, rather than lipid A or lipid-A-associated protein. The relevance of this finding to the nature of the genetic defect of xid-mice is discussed.

Idiotype profile of an immune response. II. Reversal of the relative dominance of major and minor cross-reactive idiotypes in arsonate-specific T-independent responses.

Two different cross-reactive idiotype (CRI) groups are distinguishable in the Ab response of A/J mice to the p-azobenzenearsonate (ABA) hapten: CRIA and CRIm. These two groups showed distinct patterns of relative dominance in the ensuing response depending on whether the inducing Ag was a T cell-dependent (TD) form of ABA, such as ABA-KLH or ABA-CGG, or a T-independent type 1 (TI-1) form, such as ABA-Brucella abortus or ABA-lipopolysaccharide (LPS), and on whether the response was elicited in vivo or in vitro. The CRI+ component of primary in vivo plaque-forming cell (PFC) responses to TD ABA Ags was largely (greater than 90%) CRIA+ as was, to a slightly lesser extent (greater than 75%) the CRI+ portion of secondary or hyperimmune serum Ab or PFC responses to the same Ags. In contrast, in vivo primary and hyperimmune PFC responses to ABA-Bru or ABA-LPS showed a significantly lower CRIA/CRI ratio, averaging 0.5-0.6, with some individual mice giving figures as low as 0.2, indicating predominance of CRIm over CRIA. Serological analysis of hyperimmune anti-ABA Abs from a group of 5 A/J mice immunized with ABA-Bru gave a figure of less than 0.5 for the CRIA/CRI ratio. The most striking disparity from the TD pattern was seen in primary in vitro PFC responses to the TI ABA Ags; here ratios of less than 0.2 were generally seen. Since T cell removal did not alter the Id pattern in the TI responses, CRIA-specific Ts cells do not account for the weak expression of CRIA in such responses. We propose a model that explains these results on the basis of differential expression of IdX dominance by two distinct B cell subpopulations--equatable to the Lyb-5+ and Lyb-5- B cell subsets--along with differential relative activation of these subsets in different types of responses. Examination of anti-ABA PFC responses of F1 progeny of CBA/N and A/J mice to ABA-Bru lends support to this hypothesis since CRIA expression was significantly lower in mice with the xid defect.

Low-level hypermutation in T cell-independent germinal centers compared with high mutation rates associated with T cell-dependent germinal centers.

Exceptionally germinal center formation can be induced without T cell help by polysaccharide-based antigens, but these germinal centers involute by massive B cell apoptosis at the time centrocyte selection starts. This study investigates whether B cells in germinal centers induced by the T cell-independent antigen (4-hydroxy-3-nitrophenyl)acetyl (NP) conjugated to Ficoll undergo hypermutation in their immunoglobulin V region genes. Positive controls are provided by comparing germinal centers at the same stage of development in carrier-primed mice immunized with a T cell-dependent antigen: NP protein conjugate. False positive results from background germinal centers and false negatives from non-B cells in germinal centers were avoided by transferring B cells with a transgenic B cell receptor into congenic controls not carrying the transgene. By 4 d after immunization, hypermutation was well advanced in the T cell-dependent germinal centers. By contrast, the mutation rate for T cell-independent germinal centers was low, but significantly higher than in NP-specific B cells from nonimmunized transgenic mice. Interestingly, a similar rate of mutation was seen in extrafollicular plasma cells at this stage. It is concluded that efficient activation of hypermutation depends on interaction with T cells, but some hypermutation may be induced without such signals, even outside germinal centers.

The absence of Tssc6, a member of the tetraspanin superfamily, does not affect lymphoid development but enhances in vitro T-cell proliferative responses.

The tetraspanins are a family of integral membrane proteins with four transmembrane domains. These molecules form multimolecular networks on the surfaces of many different cell types. Gene-targeting studies have revealed a role for tetraspanins in B- and T-lymphocyte function. We have isolated and deleted a novel tetraspanin, Tssc6, which is expressed exclusively in hematopoietic and lymphoid organs. Using a gene-trapping strategy, we generated an embryonic stem (ES) cell line with an insertion in the Tssc6 locus. Mice were derived from these ES cells and, using RNase protection and reverse transcription-PCR, we demonstrated that the insertion resulted in a null mutation of the Tssc6 allele. Mice homozygous for the gene trap insertion (Tssc6(gt/gt) mice) were viable and fertile, with normal steady-state hematopoiesis. Furthermore, responses to hemolysis and granulocyte colony-stimulating factor-induced granulopoiesis were equivalent to those of wild-type mice. Lymphoid development was normal in Tssc6(gt/gt) mice. Whereas Tssc6(gt/gt) B cells responded normally to lipopolysaccharide, anti-CD40, and anti-immunoglobulin M stimulation, Tssc6(gt/gt) T cells showed enhanced responses to concanavalin A, anti-CD3, and anti-CD28. This increased proliferation by Tssc6-deleted T lymphocytes was due to increased interleukin 2 production following T-cell receptor stimulation. These results demonstrate that Tssc6 is not required for normal development of the hematopoietic system but may play a role in the negative regulation of peripheral T-lymphocyte proliferation.

Antibody structural variation in rainbow trout fluids.

Rainbow trout (Oncorhynchus mykiss) were immunized with trinitrophenylated-keyhole limpet hemocyanin (TNP-KLH) and the redox structure of induced anti-TNP antibodies from the serum, mucus, egg and ovarian fluid was examined. In conducting these studies it was determined that all TNP-specific antibody from each source possessed the mAb-specific H chain (1-14) epitopes, which facilitated the direct structural analysis of the induced antibodies. A protocol was developed which ensured complete adsorption of all specific anti-TNP antibody from each fluid. Together these protocols permitted the unbiased compositional analysis of all redox forms of the anti-TNP antibodies from each source. All antibodies, regardless of source, possessed the same molecular mass, characteristic of the trout tetramer (800 kDa). It was found that specific antibody titers were significantly higher in male than female trout, while the degree of disulfide polymerization was relatively invariant in male antibodies, while being highly variable in female antibodies. Within the females, no distinctively different redox ratios were between antibodies isolated from sera, ovarian fluid or eggs: however, mucus antibodies possessed a unique redox structure consisting of halfmeric constituents that were not observed in antibodies from other fluids.

Antibody formation in mouse bone marrow during secondary type responses to various thymus-independent antigens.

The data presented in this paper show that different thymus-independent (TI) antigens have a differential capacity of inducing antibody formation in mouse bone marrow, both after primary and secondary intravenous immunization. Primary immunization with certain TI antigens (e.g., lipopolysaccharide [LPS], TNP-LPS, DNP-Ficoll) induces the appearance of antibody-forming cells not only in the spleen, but also in the bone marrow. A single injection of certain other TI antigens (e.g., pneumococci [Pn], TNP-conjugated detoxified LPS [TNP-dLPS], TNP-conjugated Brucella abortus bacteria [TNP-BA] ), on the other hand, induces antibody formation in the spleen only. After secondary immunization with these TI antigens only TNP-BA induces a PFC response in the bone marrow. Pn, TNP-dLPS and TNP-BA, but also DNP-Ficoll, are unable to induce bone marrow antibody formation after secondary injection of the antigen, in spite of the clear-cut secondary type character of the splenic response. Thus, the absence of a bone marrow PFC response after secondary immunization with these antigens is not due to a failure to induce memory B cells. This data implies that either two subpopulations of memory B cells exist, one giving rise to antibody formation in the spleen and the other accounting for the bone marrow response, or that antibody can selectively inhibit the secondary bone marrow antibody response to certain TI antigens.

Repeated high dose oral exposure or continuous subcutaneous infusion of 2-methoxyacetic acid does not suppress humoral immunity in the mouse.

2-Methoxyethanol (ME) has been shown to be immunosuppressive in rats but not mice, with oxidation of ME to 2-methoxyacetic acid (MAA) being a prerequisite for immunosuppression. MAA is more rapidly cleared by mice than rats, consequently this study was designed to determine if increasing the bioavailability of MAA in mice might play a role in this species difference. Female B6C3F1 mice were given MAA by oral multiple daily high doses or by continuous subcutaneous infusion via mini-osmotic pumps. Humoral immunity was evaluated in MAA-exposed mice using the plaque-forming cell (PFC) response to either sheep red blood cells (SRBC) or trinitrophenyl-lipopolysaccharide (TNP-LPS). Female F344 rats were also used to compare the effects of multiple daily MAA exposure on these humoral immune responses. Rats and mice were dosed orally twice a day for 4 days by gavage with MAA at dosages ranging from 40-320 mg/kg/day and 240-1920 mg/kg/day, respectively. All animals were immunized on the first day of dosing and body and lymphoid organ weights and PFC responses to SRBC or TNP-LPS were evaluated 4 days later. While body weights in rats were unaffected, thymus weights were reduced at all dosages of MAA and spleen weights were reduced at 160 or 320 mg/kg/day. PFC responses to SRBC and TNP-LPS were suppressed in rats at dosages of 160 and 320 mg/kg/day. In contrast, thymus weights of mice were reduced only at 960 mg/kg/day or greater, with no effect on spleen or body weights. Furthermore, neither the PFC response to SRBC nor the response to TNP-LPS was suppressed in mice exposed to any oral dosage of MAA. In the continuous infusion study, mice were subcutaneously implanted with mini-osmotic pumps containing MAA which was delivered at 840 mg/kg/day over a 7-day period. Continuous exposure to MAA via mini-osmotic pumps did not suppress the PFC response to either SRBC or TNP-LPS, but rather significantly enhanced the response to TNP-LPS. These results indicate that mice are insensitive to MAA even at the high dosages given as a bolus or continuously over 1 week. The data further support earlier work, which suggested that the observed difference between rats and mice for MAA-induced immunosuppression appears to be unrelated to the availability of MAA to target lymphoid tissue in these rodent species.

Effects of route of immunization, adjuvant and unrelated antigens on the humoral immune response in lines of chickens selected for antibody production against sheep erythrocytes.

Effects of intramuscular (i.m.), intravenous (i.v.) and intraperitoneal (i.p.) primary immunization with the T-dependent antigen, sheep red blood cells (SRBC), was studied in two chicken lines selected for either high (H) or low (L) antibody response after i.m. immunization with SRBC. The primary route of immunization affected the line differences in the primary response and in the secondary response after i.m. reimmunization. Intravenous immunization with the T-dependent antigen bovine serum albumin (BSA) showed line differences similar to those found after i.m. or i.v. immunization with SRBC. Immunization with both the partially T-independent antigens Brucella abortus (BA) or Salmonella H-antigen (SHA) revealed no line effect. Immunization with SRBC in incomplete Freund's adjuvant (IFA) did not change the difference between lines, whereas immunization with complete Freund's adjuvant (CFA) diminished the difference between lines. It is postulated that differences in antibody production between the selected lines might be attributed to differences in T-cell activity.

A purified saponin acts as an adjuvant for a T-independent antigen.

Three strains of mice were injected with a T-independent antigen, Escherichia coli 055:B5 polysaccharide (PS) combined with purified saponin, QS-21, isolated from Quillaja saponaria bank. PS was prepared by hydrolysis of lipopolysaccharide (LPS). Nine week old mice were injected intradermally with 60 micrograms PS, as determined by an anthrone assay, with or without 15 micrograms QS-21 on days 0 and 14. On day 22 sera were assayed by EIA for PS specific antibodies. Titers were 11-fold higher in CD-1 mice with QS-21. C3H/HeJ (Ipsd) and C3H/HeSnJ (Ipsr) mice also showed an adjuvant associated increase in titer with saponin. Therefore, LPS responsiveness was not required for the adjuvant effect. PS vaccinated C3H and CD-1 mice with and without QS-21 had similar antibody isotype profiles. IgG2b titers accounted for more than half of the total Ig response. IgG2a was next highest followed by IgG3, IgM, IgG1, and IgA. In comparison, CD-1 mice injected with 0.1 microgram intact LPS had a different LPS specific isotype profile. IgG3 was the highest followed by IgG1, IgG2b, IgM, IgG2a, and IgA.

Nasal cholera toxin elicits IL-5 and IL-5 receptor alpha-chain expressing B-1a B cells for innate mucosal IgA antibody responses.

In this study, we examine whether native cholera toxin (nCT) as a mucosal adjuvant can support trinitrophenyl (TNP)-LPS-specific mucosal immune responses. C57BL/6 mice were given nasal TNP-LPS in the presence or absence of nCT. Five days later, significantly higher levels of TNP-specific mucosal IgA Ab responses were induced in the nasal washes, saliva, and plasma of mice given nCT plus TNP-LPS than in those given TNP-LPS alone. High numbers of TNP-specific IgA Ab-forming cells were also detected in mucosal tissues such as the nasal passages (NPs), the submandibular glands (SMGs), and nasopharyngeal-associated lymphoreticular tissue of mice given nCT. Flow cytometric analysis showed that higher numbers of surface IgA+, CD5+ B cells (B-1a B cells) in SMGs and NPs of mice given nasal TNP-LPS plus nCT than in those given TNP-LPS alone. Furthermore, increased levels of IL-5R alpha-chain were expressed by B-1a B cells in SMGs and NPs of mice given nasal TNP-LPS plus nCT. Thus, CD4+ T cells from these mucosal effector lymphoid tissues produce high levels of IL-5 at both protein and mRNA levels. When mice were treated with anti-IL-5 mAb, significant reductions in TNP-specific mucosal IgA Ab responses were noted in external secretions. These findings show that nasal nCT as an adjuvant enhances mucosal immune responses to a T cell-independent Ag due to the cross-talk between IL-5Ralpha+ B-1a B cells and IL-5-producing CD4+ T cells in the mucosal effector lymphoid tissues.

Antibody repertoire development in fetal and neonatal piglets. IX. Three pathogen-associated molecular patterns act synergistically to allow germfree piglets to respond to type 2 thymus-independent and thymus-dependent antigens.

Newborn piglets maintained germfree (GF) cannot respond to either thymus-dependent (TD) or type 2 thymus-independent Ags (TI-2) unless colonized with bacteria. We show here that pathogen-associated molecular patterns (PAMPs), including muramyl dipeptide (MDP), LPS, and a B-class CpG oligonucleotide (CpG-B), can substitute for gut flora in the induction of neonatal immunoresponsiveness. These PAMPs alone or in combination had little effect on serum IgG and IgA levels, but CpG-B and CpG-B + MDP elevated total IgM levels 3- to 7-fold above that seen in colonized controls after booster immunization. Although only CpG-B could alone stimulate immunoresponsiveness, co-administration of LPS or MDP resulted in a 5-fold increase in the IgG response to both immunogens. Co-administered MDP did not promote secondary IgG responses to either Ag but instead pronounced secondary IgM responses to the epitopes of both immunogens. LPS co-administered with CpG-B may promote class switch recombination or cause differentiation of previously switched cells that become responsive after exposure to CpG-B. Primary and secondary IgG responses equally recognized the epitopes of the TI-2 and TD immunogens, whereas IgM responses favored the TI-2 epitope. Because PAMPs alone can result in Abs to 2,4,6-triitrophenyl and FLU without immunization, it suggests they alone cause differentiation of B cells of the preimmune repertoire. The finding that both bacterial PAMPs and colonization are capable of stimulating Ab responses in both immunized and nonimmunized piglets suggests that PAMPs derived from host flora may play a major role in awakening adaptive immunity in neonates.

Accessory cell defect in unresponsiveness of neonates and aged to polysaccharide vaccines.

T independent antigens elicit antibody responses in the absence of carrier specific T helper cells but require signals from accessory cells (macrophages and dendritic cells) or specific cytokines. They are further subdivided into TI-1 and TI-2 categories based on the ability of TI-1 but not TI-2 antigens to elicit immune responses from neonates. Most bacterial polysaccharides including the pneumococcal polysaccharide vaccines belong to the TI-2 class. It is hypothesized that defects in accessory cell function play a critical role in the failure of neonates to respond to such TI-2 antigens. Immune responses to these TI-2 stimuli are also reduced in the aged, also due to a quantitative deficiency in accessory cells. Agents that can stimulate accessory cell function may provide an alternative strategy to improve the immunogenicity of the polysaccharide vaccines in the neonates and the aged.

Thymus-independent induction and antigen-dependent recovery of idiotype-specific suppression.

BALB/c nude (nu/nu) mice and euthymic (nu/+) littermates were treated as neonates with anti-T15 antibody and challenged at various ages with either a thymus-independent, PC-Brucella abortus (PC-BA), or thymus-dependent, PC-keyhole limpet hemocyanin (PC-KLH), form of phosphorylcholine (PC). Nu/nu mice challenged with PC-KLH received KLH-primed splenic T cells prior to immunization. Neither neonatally anti-idiotype-treated nu/+ nor nu/nu mice responded with the production of T15-positive anti-PC antibodies after challenge with either form of PC antigen. It is concluded that neither induction nor maintenance of a state of T15-specific suppression requires thymus-matured T cells. Recovery of anti-PC responsiveness in suppressed nu/+ or nu/nu mice was similar and was found to be related to the form of antigen used to elicit the response. Immunization with PC-KLH revealed a long-lasting unresponsiveness (up to 16 weeks). In contrast, immunization with PC-BA elicited a full anti-PC response as early as at 6.5 weeks of age.

Acute and long-term effects of stressors on pulmonary immune functions.

To study the effects of different types or intensities of stressors on immune reactivity in the lungs, we studied the ex vivo production of nitric oxide (NO) and IL-1beta by alveolar macrophages (AM) after short exposure of rats to restraint stress or inescapable electric footshocks. Exposure to electric footshocks of various intensities resulted in an intensity-dependent decrease in NO production whereas the IL-1beta production by AM had increased. The secretory activity was similarly affected by restraint stress. When the time course of electric footshocks on secretory functions of AM was studied, it was found that the effects on NO and IL-1beta production by AM were normalized 3 days after the stress induction, but reappeared when cells were isolated 1 to 2 wk after stress exposure. Analysis of the effects of electric footshocks of various intensities on antibody production 10 days after the stress session and subsequent lung immunization with trinitrophenyl conjugated keyhole limpet hemocyanin (TNP-KLH), showed a footshock intensity-dependent response. Although exposure to stress induced an increase in plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT), hormone levels did not differ between the various stress-exposed groups. This suggests that the observed stress effects on pulmonary immune functions were not mediated by ACTH or CORT but point to a direct involvement of the autonomic nervous system.

Rational design of conjugate vaccines.

Whereas bacterial polysaccharides, classified as T-cell-independent antigens, elicit protective antibodies in adults, booster injections fail to produce an augmented response or promote antibody class switching. Because T-cell-dependent antigens, typically proteins, both produce boosted antibody levels and promote antibody class switching, it has been considered highly desirable to attempt to convert the T-cell-independent polysaccharide antigens into T-cell-dependent antigens, particularly for use in high-risk groups. A number of clinical trials now report the efficacy of conjugate vaccines in inducing the production of antibody in response to a number of previously poorly immunogenic--mainly T-cell-independent--antigens. In addition to conjugate vaccines containing bacterial polysaccharides, vaccines containing relevant peptides from a variety of pathogens are also being formulated and investigated. Questions remain, however, regarding their synthesis, use, and efficacy. The best ages for vaccine administration and selection of the optimal protein carrier are still under investigation, as are questions regarding the use of adjuvants, which can greatly affect the vaccine's potency. Spacing and size of epitope and size and composition of the final structure also must be considered; the importance of molecular size and aggregation of antigen in increasing immunogenicity have been well documented. These questions must be addressed for the much-needed development of conjugate vaccines against some common infections worldwide, including malaria, bacterial meningitis, and infections from Pseudomonas aeruginosa and Neisseria gonorrhoeae because of increasing susceptibility to these infections and resistance of the pathogens to chemotherapeutic agents and/or antibiotics.

Lack of general immunosuppression during visceral Leishmania tropica infection in BALB/c mice: augmented antibody response to thymus-independent antigens and polyclonal activation.

Leishmania tropica causes a lethal visceral disease in highly susceptible BALB/c mice, with many immunopathologic features resembling those in human kala-azar. The responses to thymus-independent antigens of Type 1 and 2 (TI-1, TI-2) were compared in infected mice of susceptible BALB/c and resistant C57BL/6 strains at various times after infection. The infected BALB/c mice had an augmented response to both types of antigens at 45 days after infection. Later (day 76), the response to trinitrophenylated lipopolysaccharide (TNP-LPS, a TI-1 antigen) was diminished but that to dinitrophenylated Ficoll (DNP-Ficoll, a TI-2 antigen) remained statistically above the response of uninfected mice. The response of the resistant strain to either antigen was not modified as a result of the infection. Both strains showed significant polyclonal activation, which was considerably greater in the BALB/c than in the C57BL/6 mice. The observations presented here are in contrast to the widely held belief that a generalized nonspecific immunosuppression occurs in L. tropica infected BALB/c mice.