InVivoMAb anti-mouse MHC Class I (H-2Kb/H-2Db)

Eleven hybridoma antibodies directed against mouse major histocompatibility complex products of the H-2b haplotype have been produced and characterized. Of 7 antibodies reacting to H-2Kb and/or H-2Db antigens, all cross-reacted with other H-2 antigens, and 5 exhibited no correspondence with a known H-2 specificity established in the H-2 chart. Four anti-Iab antibodies all reacted with antigens encoded by the I-A subregion. Some of these antibodies showed no cross-reaction with other haplotypes, indicating reactions to private specificities of the I-Ab antigen. In addition, these anti-Ia antibodies appeared to be capable of distinguishing fine determinant differences, which corresponding alloantisera failed to reveal. A high frequency of hybridomas secreting IgM antibodies was found after fusions of spleen cells obtained from C3H anti-C3H.SW immunized mice, in contrast to the dominance of IgG hybridomas produced previously by fusions of spleen cells from mice immunized in the reverse direction. An isotype analysis of conventional cytotoxic alloantisera from the same strain combinations was therefore performed. The same correlation with respect to isotype expression was found, indicating that hybridoma antibodies reflect normal antibody responses and suggesting H-2-linked control of this expression.

The role of major histocompatibility complex (MHC) class I- and class II-restricted functions in Helicobacter pylori infection and immunity upon oral immunization was examined in vivo. Experimental challenge with H. pylori SS1 resulted in significantly greater (P </= 0.025) colonization of MHC class I and class II mutant mice than C57BL/6 wild-type mice. Oral immunization with H. pylori whole-cell lysates and cholera toxin adjuvant significantly reduced the magnitude of H. pylori infection in C57BL/6 wild-type (P = 0.0083) and MHC class I knockout mice (P = 0.0048), but it had no effect on the H. pylori infection level in MHC class II-deficient mice. Analysis of the anti-H. pylori antibody levels in serum showed a dominant serum immunoglobulin G1 (IgG1) response in immunized C57BL/6 wild-type and MHC class I mutant mice but no detectable serum IgG response in MHC class II knockout mice. Populations of T-cell-receptor (TCR) alphabeta+ CD4(+) CD54(+) cells localized to gastric tissue of immunized C57BL/6 wild-type and MHC class I knockout mice, but TCRalphabeta+ CD8(+) cells predominated in the gastric tissue of immunized MHC class II-deficient mice. These observations show that CD4(+) T cells engaged after mucosal immunization may be important for the generation of a protective anti-H. pylori immune response and that CD4(+) CD8(-) and CD4(-) CD8(+) T cells regulate the extent of H. pylori infection in vivo.

Cytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC). The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes. However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood. H-2b beta 2-microglobulin-deficient mice (beta 2M-/-) are not able to produce CD8+ CTL in response to infection with L. monocytogenes. We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L. monocytogenes. We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4+ class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L. monocytogenes in the spleen was found established infection. In beta 2M-/- mice, persistence of L. monocytogenes in the spleen was found preferentially in class II-negative cells. Surprisingly, class I-restricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from beta 2M-/- mice. These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class II-restricted cytotoxic response may escape prompt eradication by the immune system.

We transfected the mouse IFN-gamma and/or the mouse B7 (T cell costimulatory molecule) cDNAs into B16 melanoma cells to study the effects of local constitutive expression of these molecules on the tumorigenicity and immunogenicity of this aggressive tumor. Cells expressing IFN-gamma (B16.IFN-gamma), B7 (B16.B7), B7 and IFN-gamma (B16.IFN-gamma/B7), and parental cells were injected subcutaneously (s.c.) into syngeneic C57BL/6 mice to compare their in vivo growth. We report that IFN-gamma secretion significantly reduced the tumorigenicity of B16 cells. These effects were related to the direct action of secreted IFN-gamma since i) in vivo injection of antiserum to IFN-gamma accelerated tumor growth, ii) development of tumor correlated with loss of IFN-gamma production, and iii) B16.IFN-gamma cells were tumorigenic in IFN-II receptor (IFN-gamma R) knockout mice, but not in parental mice. We propose that immune mechanisms are being activated by IFN-gamma since i) immune effector cells were recruited to the injection site, ii) expression of MHC class I and class II antigens was increased on cells secreting IFN-gamma and, iii) B16.IFN-gamma tumors appeared earlier in athymic mice than in immunocompetent mice. Since the in vivo growth of B16.IFN-gamma cells was not completely abolished, we studied the effect of co-expression of IFN-gamma and the T cell costimulatory molecule B7 on the tumorigenicity of B16 cells. We report that B16.IFN-gamma/B7 cells, which also express increased levels of MHC class I and class II molecules as compared to parental cells, had a dramatically suppressed tumorigenicity, while B16 cells expressing the B7 molecule only (B16.B7) were as tumorigenic as the parental cells. B16.IFN-gamma/B7 cells induced specific immune responses since all of the protected mice were able to reject challenges with parental cells. Results indicate that co-expression of two molecules which are involved in the activation of immune responses and in antigen presentation can influence the ability of the immune system to recognize and eliminate both transfected as well as parental tumor cell inocula and suggest that vaccines consisting of such cells may be used for the immunotherapy of cancer.