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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.

Lines of mice selected for high or low antibody production to sheep red blood cells (H-I and L-I) were studied for their ability to process and present ovalbumin to a panel of 12 T-T hybridomas in two different H-2 haplotypes. When H-I and L-I spleen cells were used as antigen-presenting cells, no difference could be observed in the peptide generation by these mice compared to H-2-compatible B.10.Q and B.10.S spleen cells, respectively. Neither normal splenic L-I B-cells nor L-I thioglycolate-induced peritoneal macrophages were defective at presenting native ovalbumin, to six and eight different I-As-restricted T-T hybrids, respectively. Altogether, these results differ from previous findings which had indicated a deficiency in the processing and presentation of antigen by the low line, L-I.

H-I and H-II high antibody-responder Biozzi mice, which express the H-2q permissive haplotype, were shown to be sensitive and refractory to collagen-induced arthritis, respectively. To assess a possible role of T cell receptor (TcR) V beta gene deletion or polymorphism in the resistance to arthritis in H-II mice, the germinal structure of TcR V beta genes and their expression at the membrane level were compared in both lines. In contrast to H-2q refractory SWR mice, which exhibit a deletion of about 50% of TcR V beta gene segments. H-I and H-II lines have an identical and complete set of V beta genes and exhibit no difference in the average expression of V beta 6, V beta 8 and V beta 11 gene products on T cell surface. These results indicate that mechanisms other than V beta gene deletion or polymorphism can be involved in the resistance of H-2q-positive mice to experimental arthritis.