C57BL/10 and BALB/c mice differ in their abilities to clear infections with the intracellular bacterium Brucella abortus strain 2308. We have previously reported that in vivo of IL-10 in the susceptible BALB/c mice results in significantly fewer bacteria in their spleens 1 week after infection with 5 x 10(3) colony forming units (CFU) of 2308. Here we extend those studies and report a similar effect when IL-4 is neutralized. In contrast, in the more resistant C57BL/10 mice infected with 5 x 10(3) CFU, neither neutralization of IL-4 significantly decreased the level of infection nor did it in either BALB/c or C57BL/10 mice infected with a 1000-fold higher dose of strain 2308. While splenocytes from the later mentioned groups of mice produced IL-10 in response to stimulation with brucella antigen, they also produced higher levels of interferon (IFN)-gamma than those from BALB/c mice with the low challenge dose of 5 x 10(3) CFU. Results of in vivo neutralization of IFN-gamma by monoclonal antibodies (MAb) reported here and elsewhere indicated that IFN-gamma is important for control; thus, we postulate that the higher levels of IFN-gamma override the detrimental effects of Th2 cytokines. In vitro studies also showed that macrophages from the more resistant C57BL/10 mice were less susceptible to the ability of IL-10 to decrease anti-brucella activities than were BALB/c macrophages. CD4+ T cells were principally responsible for the production of IL-10 in BALB/c but not C57BL/10 splenocyte populations. C57BL/10 splenocytes produced more IFN-gamma than those from BALB/c mice in response to stimulation with brucella antigens. These differences between BALB/c and C57BL/10 mice may contribute to the superior capacity of C57BL/10 mice to control infections with B. abortus strain 2308.

In vivo neutralization of interleukin-10 (IL-10) with an anti-IL-10 monoclonal antibody resulted in up to 10-fold fewer bacteria in the spleens of BALB/c mice infected with the virulent Brucella abortus strain 2308. In vitro neutralization of endogenous IL-10 in brucella antigen-stimulated cultures of splenocytes from infected mice resulted in increased gamma interferon production in these cultures, whereas exogenous recombinant IL-10 inhibited the ability of peptone-elicited peritoneal macrophages to control intracellular brucellae. These data suggest that IL-10 may be downregulating the immune response to B. abortus by affecting both macrophage effector function and the production of the protective Th1 cytokine gamma interferon.

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We evaluated the capacity of the secretory pathway or of different endocytic compartments in B cell lines to generate MHC class II‐presented peptides from the antigen ovalbumin (OVA). Sorting signals from the transferrin receptor (TFR), targeted a chimeric OVA fusion protein to early endosomes and led to the generation of 8 of 12 presented peptides. Sorting signals from the lysosome‐associated membrane protein 1 (LAMP‐1), targeted an OVA fusion protein to lysosomes, and led to the generation of 9 of 12 peptides. In contrast, OVA with only a signal sequence led to the generation of only 2 presented peptides. There were both qualitative and quantitative differences in the generation of peptides from the different fusion proteins, suggesting that multiple distinct compartments are involved in generating different epitopes. One peptide was presented better from the TFR fusion protein, while all others were presented better from the LAMP‐1 construct. Twelve peptides were generated from exogenously supplied OVA, including 3 peptides that were not generated from any of the fusion proteins. Since most endogenously synthesized foreign antigens are rarely presented on class II molecules, these studies further suggest a strategy whereby antigens in DNA‐based vaccines could be targeted to endocytic compartments to enhance immunogenicity.