MyD88 signaling is not essential for induction of antigen-specific B cell responses but is indispensable for protection against Streptococcus pneumoniae infection following oral vaccination with attenuated Salmonella expressing PspA antigen

TLRs directly induce innate host defense responses, but the mechanisms of TLR-mediated adaptive immunity remain subject to debate. In this study, we clarified a role of TLR-mediated innate immunity for induction of adaptive immunity by oral vaccination with a live recombinant attenuated Salmonella enteric serovar Typhimurium vaccine (RASV) strain expressing Streptococcus pneumoniae surface protein A (PspA) Ag. Of note, oral or intranasal vaccination with RASV expressing PspA resulted in identical or even significantly higher levels of PspA-specific IgG and IgA responses in the systemic and mucosal compartments of MyD88(-/-) mice of either BALB/c or C57BL/6 background when compared with those of wild-type mice. Although PspA-specific CD4(+) T cell proliferation in the MyD88(-/-) mice was minimal, depletion of CD4(+) T cells abolished PspA-specific IgG and IgA responses in the MyD88(-/-) mice of BALB/c background. Of the greatest interest, MyD88(-/-) mice that possessed high levels of PspA-specific IgG and IgA responses but minimal levels of CD4(+) T cell responses died earlier than nonvaccinated and vaccinated wild-type mice following i.v. or intranasal challenge with virulent S. pneumoniae. Taken together, these results suggest that innate immunity activated by MyD88 signals might not be necessary for Ag-specific Ab induction in both systemic and mucosal sites but is critical for protection following oral vaccination with attenuated Salmonella expressing PspA.     

IgA immunodeficiency leads to inadequate Th cell priming and increased susceptibility to influenza virus infection

IgA is considered to be the principal Ab involved in defense against pathogens in the mucosal compartment. Using mice with a targeted disruption in IgA gene expression (IgA(-/-) mice), we have examined the precise role of IgA in protective anti-influenza responses after intranasal vaccination. IgA(-/-) mice immunized intranasally with soluble hemagglutinin (hemagglutinin subtype 1) and neuraminidase (neuraminidase subtype 1) vaccine in the absence of adjuvant were found to be more susceptible to influenza virus infection than IgA(+/+) mice (13 vs 75% survival after virus challenge). Inclusion of IL-12 during immunization restored the protective efficacy of the vaccine to that seen in IgA(+/+) animals. IgA(-/-) mice had no detectable IgA expression, but displayed enhanced serum and pulmonary IgM and IgG Ab levels after IL-12 treatment. Assessment of T cell function revealed markedly depressed splenic lymphoproliferative responses to PHA in IgA(-/-) animals compared with IgA(+/+) mice. Furthermore, IgA(-/-) animals displayed impaired T cell priming to the H1N1 subunit vaccine, with concomitant reduction in recall memory responses due to a defect in APC function. Collectively, these results provide evidence that a major role of IgA is to facilitate presentation of Ag to mucosal T cells. IL-12 treatment can overcome IgA deficiency by providing adequate T cell priming during vaccination.     

Host defence against C. albicans infections in IgH transgenic mice with V(H) derived from a natural anti-keratin antibody

Fungal infections have been increasing and life-threatening in recent years, but host immune responses, especially the humoral immunity, to fungi have not been fully understood. In the present study, we report that natural antibodies from unimmunized mice bind to Candida albicans. We established a monoclonal natural antibody, 3B4, which recognized a surface antigen located at germ tubes of C. albicans. The 3B4 antibody protected mice from C. albicans-induced death in passive immunization, by mechanisms involving suppressing germ tube formation and modulating phagocytosis. Interestingly, 3B4 also bound to a self-antigen keratin. To further study the generation and anti-C. albicans activities of natural antibodies in vivo, we constructed a mu chain transgenic mouse (TgV(H)3B4) using the V(H) gene from 3B4. TgV(H)3B4 had elevated serum anti-keratin/C. albicans IgM, and were resistant to C. albicans infections. Analyses of B cell development showed that in TgV(H)3B4, B cells secreting the anti-keratin/C. albicans antibodies were enriched in the B1 B cell compartment. Our findings reveal an important role of keratin-reactive natural antibodies in anti-C. albicans immune responses, and suggest that keratin may function in selecting B cells into the B1 B cell compartment, where natural antibodies are made to fight fungal infections.     

Murine defense mechanism against Candida albicans infection. I. Collaboration of cell-mediated and humoral immunities in protection against systemic C. albicans infection

Mice immunized with viable C. albicans cells demonstrated a high incidence of cell-mediated and a low incidence of humoral immune response. There was good agreement between the final survival rate of C. albicans infected mice and the rate of simultaneous cell-mediated and humoral immune response acquisition. Immunized mice with positive delayed hypersensitivity (DTH) against C. albicans crude antigen showed significant protection against intravenous challenge with C. albicans. Furthermore, the transfer of immunoglobulins from rabbit anti-C. albicans serum to DTH-positive mice enhanced protection, while it did not protect control mice against a subsequent challenge with C. albicans. These results suggest that cell-mediated immunity plays a major role and humoral immunity a side role in the defense mechanism(s) of C. albicans infected mice.     

Toll-like receptor-2 is essential in murine defenses against Candida albicans infections

In this work, we studied the role of toll-like receptor-2 (TLR2) in murine defenses against Candida albicans. TLR2-deficient mice experimentally infected intraperitoneally (i.p.) or intravenously (i.v.) in vivo had very significant impaired survival compared with that of control mice. In vitro production of TNF-alpha and macrophage inhibitory protein-2 (MIP-2) by macrophages from TLR2-/- mice in response to yeasts and hyphae of C. albicans were significantly lower (80% and 40%, respectively; P <0.05) than production by macrophages from wild-type mice. This impaired production of TNF-alpha and MIP-2 probably contributed to the 41% decreased recruitment of neutrophils to the peritoneal cavity of i.p. infected TLR2-/- mice. In contrast, in vitro phagocytosis of yeasts and production of reactive oxygen intermediates (ROI) were not affected in macrophages from TLR2-/- animals. Our data indicate that TLR2 plays a major role in the response of macrophages to C. albicans, triggering cytokine and chemokine expression, and it is essential for in vivo protection against infection.     

Chlamydia trachomatis pulmonary infection induces greater inflammatory pathology in immunoglobulin A deficient mice

Chlamydia trachomatis is an intracellular bacterial pathogen that primarily infects via mucosal surfaces. Using mice with a targeted disruption in IgA gene expression (IgA(-/-) mice), we have studied the contribution of IgA, the principal mucosal antibody isotype, in primary immune defenses against pulmonary C. trachomatis infection. Bacterial burden was comparable between IgA(-/-) and IgA(+/+) animals following C. trachomatis challenge. Serum and pulmonary anti-Chlamydia antibody levels were higher in IgA(-/-) animals, with the exception of IgA. Lung sections of challenged IgA(-/-) mice showed more extensive immunopathology than corresponding IgA(+/+) animals. Real-time PCR analysis demonstrated significantly greater IFN-gamma and TGF-beta mRNA expression in IgA(-/-) as compared to IgA(+/+) animals. Together, these results suggest that IgA may not be necessary for clearance of primary C. trachomatis infection. However, IgA(-/-) mice displayed exaggerated lung histopathology and altered cytokine production, indicating an important role for IgA in regulating C. trachomatis induced pulmonary inflammation and maintenance of mucosal homeostasis.     

Early local generation of C5a initiates the elicitation of contact sensitivity by leading to early T cell recruitment

We have shown previously that an early complement C5-dependent cascade is required to recruit T cells to elicit 24-h contact sensitivity (CS) responses. In this paper, we have characterized molecular events of this early required cascade by biochemically analyzing extracts of mouse ears undergoing elicitation of CS. Chemotactic activity was found after local Ag challenge, in CS ear extracts early (by 1 h), in CS ear extracts late (through 24 h), in previously immunized mice, but not in ears of vehicle-immunized or non-immune-challenged mice. The early chemotactic activity at 2 h was likely caused by C5a, because it was neutralized in vitro by anti-C5a Ab, was inactive on C5aR-deficient (C5aR-/-) macrophages, and was absent in C5-deficient mice. The activity was present in T cell-deficient mice, but elaboration was Ag-specific. This T cell-independent, Ag-specific elaboration of C5a early in CS ear responses likely led to T cell recruitment, because subsequent local IFN-gamma mRNA and protein expression, as markers of T cell arrival and activation, began by 4 h after Ag challenge. In contrast to early C5a chemotactic activity, late chemotactic activity 24 h after Ag challenge was unaffected by anti-C5, was active on C5aR-/- macrophages, was T cell-dependent, and by ELISA appeared largely due to chemokines (macrophage-inflammatory protein-1alpha and -1beta, IFN-gamma-inducible protein-10, and monocyte chemoattractant protein-1). Importantly, early generation of C5a was required for T cell recruitment because C5aR-/- mice had absent 24-h CS. Taken together, these findings indicate an important linkage of C5a as a component of early activated innate immunity that is required for later elicitation of acquired T cell immunity, probably by facilitating the initial recruitment of T cells into the Ag-challenged local site in CS responses.     

Studies on the induction of tolerance to alloantigens. II. The generation of serum factor(s) able to transfer alloantigen-specific tolerance for delayed-type hypersensitivity by portal venous inoculation with allogeneic cells

The administration of C3H/He spleen cells into allogeneic BALB/c mice via portal venous (p.v.) route resulted in C3H/He alloantigen-specific tolerance for delayed-type hypersensitivity (DTH) responses. When serum from these tolerant BALB/c mice were transferred into naive syngeneic BALB/c mice, the recipient mice lost the capability of generating DTH responses as induced by s.c. immunization with C3H/He cells. Tolerance was transferred only by serum from BALB/c mice inoculated p.v. with C3H/He cells, but not by serum from C3H/He mice inoculated p.v. with C3H/He cells, or BALB/c mice inoculated i.v. with C3H/He cells. This tolerogenic activity in serum from p.v. inoculated BALB/c mice was C3H/He alloantigen specific, because the transfer of the serum did not interfere with the development of anti-C57BL/6 DTH responses in recipient BALB/c mice. Such a serum factor(s) was inducible as early as 1 wk after the inoculation of C3H/He cells into BALB/c mice and not associated with anti-C3H/He alloantibody activity. Moreover, anti-C3H/He or C57BL/6-specific tolerogenic factor(s) prepared in the respective BALB/c or C3H/He mice was successfully transferred into totally allogeneic recipient mice, indicating no requirement of H-2, as well as non-H-2 restriction for the function of serum tolerogenic factor(s). Thus this study demonstrates that p.v. inoculation of allogeneic cells generates serum factor(s) able to transfer in H-2 and non-H-2-unrestricted manners the in vivo tolerance of the alloreactivity specific for alloantigens used for p.v. inoculation.     

Studies on the induction of tolerance to alloantigens. I. The abrogation of potentials for delayed-type-hypersensitivity response to alloantigens by portal venous inoculation with allogeneic cells

The present study investigates the effect of portal venous (p.v.) administration of allogeneic cells on the capacity of delayed-type-hypersensitivity (DTH) reactivity to alloantigens. BALB/c mice were inoculated with C3H/He spleen cells via intravenous (i.v.) or p.v. route. Intravenous injection of C3H/He spleen cells into BALB/c mice resulted in appreciable DTH responses to C3H/He alloantigens. In contrast, p.v. inoculation of the same number of C3H/He cells not only failed to induce any significant anti-C3H/He DTH responses but also abolished the capability of the animals to develop DTH responses as induced by subcutaneous (s.c.) immunization with C3H/He spleen cells. Such suppression was alloantigen-specific, since p.v. inoculation of C3H/He spleen cells resulted in selective inhibition of anti-C3H/He DTH potential without suppressing DTH responses to C57BL/6 alloantigens. This tolerance was rapidly inducible and long-lasting. When spleen cells from tolerant mice were transferred i.v. into 600 R X-irradiated syngeneic recipient mice alone or together with normal BALB/c spleen cells, these tolerant spleen cells themselves failed to induce DTH responses but did not exhibit any suppressive effect on the generation of DTH responses induced by normal spleen cells co-transferred. These results indicate that tolerance was not necessarily associated with the induction of suppressor cell activity but rather was associated with the elimination or functional impairment of clones specific for alloantigens. The results are discussed in the context of a) the role of the liver in immune responses, b) cellular mechanisms underlying the tolerance induction, and c) potential application of this approach to the future transplantation immunology.     

Studies on the induction of tolerance to alloantigens. III. Induction of antibodies directed against alloantigen-specific delayed-type hypersensitivity T cells by a single injection of allogeneic lymphocytes via portal venous route

BALB/c mice were inoculated with normal C3H/He spleen cells via the portal venous (p.v.) route. Intravenous injection of serum from these BALB/c mice into naive syngeneic mice resulted in almost complete abrogation of their ability to generate anti-C3H/He delayed-type hypersensitivity (DTH) responses as induced by s.c. immunization with C3H/He cells. Since a portion of the same serum did not inhibit the development of anti-C57BL/6 DTH responses, the suppressive effect of the transferred serum was alloantigen-specific. Such serum factor(s) was produced in normal but not in nude mice and the suppressive activity was transferred in H-2- or immunoglobulin allotype-incompatible combinations. Immunochemical analyses of this serum suppressive factor have revealed that its m.w. was approximately 150,000, corresponding to the size of immunoglobulin (Ig)G, and that the activity was trapped by protein A or by an anti-immunoglobulin column. Although the absorption of the serum from anti-C3H/He-tolerant BALB/c mice with C3H/He target spleen cells did not abrogate the suppressive activity, the additional absorption with spleen cells from anti-C3H/He hyperimmune BALB/c mice almost completely eliminated the suppressive potential. Moreover, pretreatment of BALB/c anti-C3H/He DTH effector spleen cells with the above serum from tolerant mice induced the inhibition of anti-C3H/He DTH responses. Taken together, these results indicate that a single injection of allogeneic cells via the p.v. route results in the production of antibody capable of inhibiting the capacity of DTH effector cells specific for alloantigens used for the p.v. presensitization.     

IL-13 attenuates gastrointestinal candidiasis in normal and immunodeficient RAG-2(-/-) mice via peroxisome proliferator-activated receptor-gamma activation

We recently demonstrated that in vitro peroxisome proliferator-activated receptor-gamma (PPARgamma) activation of mouse peritoneal macrophages by IL-13 or PPARgamma ligands promotes uptake and killing of Candida albicans through mannose receptor overexpression. In this study, we demonstrate that i.p. treatment of immunocompetent and immunodeficient (RAG-2(-/-)) mice with natural and synthetic PPARgamma-specific ligands or with IL-13 decreases C. albicans colonization of the gastrointestinal (GI) tract 8 days following oral infection with the yeast. We also showed that Candida GI infection triggers macrophage recruitment in cecum mucosa. These mucosal macrophages, as well as peritoneal macrophages, overexpress the mannose receptor after IL-13 and rosiglitazone treatments. The treatments promote macrophage activation against C. albicans as suggested by the increased ability of peritoneal macrophages to phagocyte C. albicans and to produce reactive oxygen intermediates after yeast challenge. These effects on C. albicans GI infection and on macrophage activation are suppressed by treatment of mice with GW9662, a selective PPARgamma antagonist, and are reduced in PPARgamma(+/-) mice. Overall, these data demonstrate that IL-13 or PPARgamma ligands attenuate C. albicans infection of the GI tract through PPARgamma activation and hence suggest that PPARgamma ligands may be of therapeutic value in esophageal and GI candidiasis in immunocompromised patients.     

Effects of probiotic bacteria on humoral immunity to Candida albicans in immunodeficient bg/bg-nu/nu and bg/bg-nu/+ mice

Germfree beige-nude ( bg/bg-nu/nu) and beige-heterozygous ( bg/bg-nu/+) mice were colonized with a pure culture of Candida albicans or with a probiotic bacterium (Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus casei, or Bifidobacterium infantis). Probiotic-colonized mice were subsequently challenged orally with C. albicans. The effect of prior colonization with probiotic bacteria on the antibody responses of the immunodeficient mice to alimentary tract colonization with C. albicans was compared to the antibody responses of the gnotobiotic mice colonized only with C. albicans. This study demonstrated that, although the probiotic bacteria did not induce a vigorous antibody response to their own antigens, they altered the antibody responses of mice to C. albicans. In T cell competent bg/bg-nu/+mice, B. infantis enhanced and focused IgG1, IgG2A, and IgA responses to C. albicans antigens. Some of the probiotic bacteria also enhanced the IgG1 and IgG2A antibody responses of bg/bg-nu/nu mice to C. albicans antigens. This study not only shows the value of gnotobiotic animal models in demonstrating that probiotic bacteria can affect the capacity of mice to form antibodies to C. albicans, but it also points out their usefulness in comparing the capacity of different probiotic bacteria to produce beneficial health effects in mice.     

Suppression of splenic macrophage Candida albicans phagocytosis following in vivo depletion of natural killer cells in immunocompetent BALB/c mice and T-cell-deficient nude mice

The resistance of mice to systemic infections caused by Candida albicans is associated with activated splenic macrophages. In addition, there is a correlation between natural killer (NK) cell activation and the resistance to systemic candidiasis. The present study was designed to clarify the role of NK cells in the control of splenic macrophage C. albicans phagocytosis by either depleting NK cells (anti-asialo GM(1) treatment) or maintaining them in an activated state (tilorone treatment) in both immunocompetent BALB/c mice and T-cell-deficient nude mice. The results of the in vitro phagocytosis assays were analyzed by flow cytometry and demonstrate the pivotal role of NK cells in controlling the capacity of splenic macrophages to phagocytose C. albicans. In summary, these data provide evidence that the NK cells are the main inducers of phagocytic activity of splenic macrophages and that they mediate the protection against C. albicans systemic infection.     

Critical role of signaling through IL-1 receptor for development of arthritis and sepsis during Staphylococcus aureus infection

IL-1R-deficient mice (IL-1R(-/-)) and their wild-type controls (IL-1R(+/+)) were i.v. inoculated with 1 x 10(7) or 10(6) Staphylococcus aureus per mouse to mimic bacterial sepsis and septic arthritis. The disease outcome was severely worsened in the IL-1R(-/-) mice as compared with IL-1R(+/+) mice. Indeed, 3 days after inoculation of 10(7) S. aureus per mouse 84% of IL-1R(-/-) mice displayed clinical signs of septicemia as compared with none of the IL-1R(+/+) mice. On day 9 after inoculation with 10(6) S. aureus per mouse 75% of the IL-1R(-/-) mice were dead as compared with none of the IL-1R(+/+) mice. Also, the number of staphylococci in circulation was 25- to 30-fold increased in IL-1R(-/-) mice as compared with IL-1R(+/+) mice, the most probable reason for the outcome. The frequency and severity of septic arthritis were significantly increased in IL-1R(-/-) mice, as compared with IL-1R(+/+) mice, following i.v. inoculation of staphylococci. This was probably due to an increased accumulation of bacteria in the joints of IL-1R(-/-) mice as compared with their wild-type controls. Interestingly, while serum levels of IL-18 in IL-1R(-/-) mice were significantly lower than in IL-1R(+/+) mice 24 h after inoculation of S. aureus, both IL-18 and IL-1beta were significantly increased in IL-1R(-/-) vs IL-1R(+/+) mice 4 days after the bacterial inoculation. In conclusion, IL-1R signaling plays a crucial role in host protection during systemic S. aureus infection as seen by the fatal outcome of S. aureus sepsis and arthritis in IL-1R-deficient mice.     

Loss of pro-apoptotic Bim promotes accumulation of pulmonary T lymphocytes and enhances allergen-induced goblet cell metaplasia

Immunological tolerance during prolonged exposure to allergen is accompanied by a shift in the lymphocyte content and a reduction of goblet cell metaplasia (GCM). Bim initiates negative selection of autoreactive T and B cells and shut down of T cell immune responses in vivo. The present study investigated whether Bim plays a role in the resolution of GCM during prolonged exposure to allergen. Loss of Bim increased T lymphocyte numbers in the bronchoalveolar lavage at 4 and 15 days of allergen exposure. The numbers of pulmonary CD4(+)8(-), CD4(-)8(+), and gammadelta T cells were significantly higher in naive and allergen-challenged bim(-/-) mice compared with wild-type (WT) littermates. When activated, pulmonary bim(-/-) T cells produced increased levels of IFNgamma compared with bim(+/+) T cells. No differences were noted in the total numbers of epithelial cells per millimeter of basal lamina between bim(+/+) and bim(-/-) mice, and the rate of resolution over 15 days of exposure was similar in both groups of mice. However, GCM was significantly enhanced and expression of IL-13Ralpha2 was reduced in bim(-/-) mice compared with WT mice at 4 days. Furthermore, treatment of bronchiolar explant cultures with increasing IFNgamma levels reduced immunostaining for IL-13Ralpha2. Collectively, these studies suggest that, during prolonged exposure to allergen, Bim plays no role in the resolution of GCM, but increased IFNgamma levels in bim(-/-) mice may be responsible for reduced expression of IL-13Ralpha2 and enhanced GCM despite similar levels of IL-13 in bim(+/+) and bim(-/-) mice.     

SOCS1 is a critical inhibitor of interferon gamma signaling and prevents the potentially fatal neonatal actions of this cytokine.

Mice lacking suppressor of cytokine signaling-1 (SOCS1) develop a complex fatal neonatal disease. In this study, SOCS1-/- mice were shown to exhibit excessive responses typical of those induced by interferon gamma (IFNgamma), were hyperresponsive to viral infection, and yielded macrophages with an enhanced IFNgamma-dependent capacity to kill L. major parasites. The complex disease in SOCS1-/- mice was prevented by administration of anti-IFNgamma antibodies and did not occur in SOCS1-/- mice also lacking the IFNgamma gene. Although IFNgamma is essential for resistance to a variety of infections, the potential toxic action of IFNgamma, particularly in neonatal mice, appears to require regulation. Our data indicate that SOCS1 is a key modulator of IFNgamma action, allowing the protective effects of this cytokine to occur without the risk of associated pathological responses.     

Neutrophil Fc gamma RI as target for immunotherapy of invasive candidiasis

Invasive candidiasis represents a life-threatening disease for immunocompromised patients. This study focused on new immunotherapeutic approaches for systemic Candida albicans infections in a human FcgammaRI-transgenic mouse model. FcgammaRI (CD64) is a potent immunoactivating receptor on phagocytic and dendritic cells. In vivo targeting of C. albicans toward neutrophil-FcgammaRI by bispecific Abs and G-CSF effectively protected FcgammaRI-transgenic mice from lethal candidiasis. Nontransgenic mice were not protected, and treatment with bispecific Ab or G-CSF alone did not reduce mortality. Furthermore, infected FcgammaRI-transgenic mice developed high titers of anti-C. albicans IgG, and survival was extended on secondary infection without further treatment. These findings document the capacity of FcgammaRI to initiate potent anti-C. albicans immunity and support the development of FcgammaRI-directed immunotherapy of invasive fungal disease.     

Modulation of allergic inflammation in mice deficient in TNF receptors

Tumor necrosis factor-alpha (TNF) is implicated as an important proinflammatory cytokine in asthma. We evaluated mice deficient in TNF receptor 1 (TNFR1) and TNFR2 [TNFR(-/-) mice] in a murine model of allergic inflammation and found that TNFR(-/-) mice had comparable or accentuated responses compared with wild-type [TNFR(+/+)] mice. The responses were consistent among multiple end points. Airway responsiveness after methacholine challenge and bronchoalveolar lavage (BAL) fluid leukocyte and eosinophil numbers in TNFR(-/-) mice were equivalent or greater than those observed in TNFR(+/+) mice. Likewise, serum and BAL fluid IgE; lung interleukin (IL)-2, IL-4, and IL-5 levels; and lung histological lesion scores were comparable or greater in TNFR(-/-) mice compared with those in TNFR(+/+) mice. TNFR(+/+) mice chronically treated with anti-murine TNF antibody had BAL fluid leukocyte numbers and lung lesion scores comparable to control antibody-treated mice. These results suggest that, by itself, TNF does not have a critical proinflammatory role in the development of allergic inflammation in this mouse model and that the production of other cytokines associated with allergic disease may compensate for the loss of TNF bioactivity in the TNFR(-/-) mouse.     

Murine bone marrow IgA responses to orally administered sheep erythrocytes

Specific immunization protocols have been established for the induction of murine bone marrow IgA responses to the T cell-dependent (TD) antigen sheep red blood cells (SRBC). Systemic immunization, either i.p. or i.v., followed by a second injection, induced splenic IgM and IgG responses and a bone marrow IgM response. No significant IgA responses were observed in either lymphoid tissue compartment. Oral immunization with SRBC by gastric intubation for 2 days, followed 1 wk later by an i.p. injection of SRBC resulted in a splenic IgA plaque-forming cell (PFC) response, but did not elicit a bone marrow IgA response. Repeated daily gastric intubation of SRBC to C3H/HeN and C3H/HeJ mice led to the previously reported pattern of systemic unresponsiveness in C3H/HeN mice and good anamnestic type IgM, IgG, and IgA splenic anti-SRBC PFC responses in the C3H/HeJ strain upon parenteral challenge. Oral administration of SRBC for 14 days to C3H/HeN mice, followed by systemic SRBC challenge, resulted in diminished splenic PFC responses of all isotypes, whereas gastric intubation of SRBC for 28 days led to complete systemic unresponsiveness to antigen in C3H/HeN mice. Interestingly, the repeated oral administration of SRBC resulted in significant bone marrow IgA PFC responses upon i.p. challenge in both C3H/HeN and C3H/HeJ mouse strains. The bone marrow IgA responses were clearly dependent upon chronic oral exposure to SRBC, because gastric intubation with SRBC for 2 consecutive days/wk for 10 wk also induced bone marrow and splenic IgA anti-SRBC PFC responses in C3H/HeN mice. These results suggest that memory B cells reside in the bone marrow of orally immunized mice and can yield anamnestic-type responses to challenge with the inducing antigen. The memory cells may arise in the Peyer's patches of the gut and migrate to the bone marrow. The possibility that the bone marrow is a component of the common mucosal immune system in mammals is suggested by this study.     

Production and function of cytokines in natural and acquired immunity to Candida albicans infection.

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.