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Major histocompatibility complex antigen expression on lymphocytes from aging strain A mice.

Molecules encoded by the major histocompatibility complex (MHC) are crucial for the proper functioning of the immune response. In this study, the levels of class I and class II major histocompatibility antigens on lymphocytes from strain A mice were measured as a function of age. Class I protein levels increased significantly on both peripheral blood and spleen (T cells and B cells) lymphocytes with age. This increase in MHC class I protein levels was accompanied by an increase in class I mRNA levels. On the other hand, class II protein levels did not show a significant change with age. Moreover, while the percentage of class I-expressing spleen lymphocytes stayed at a steady-state level of 100% with age, the percentage of class II-expressing spleen lymphocytes decreased from 85% in young animals to 70% in old animals. This decrease was due to a decrease in the relative proportion of B cells compared to T cells in the spleen lymphocyte population of old mice. When class II mRNA levels were measured, it was found that these levels decreased markedly with age. Overall, it is clear that the regulation of MHC class I and class II expression changes with age in A strain mice. Since optimal levels of MHC expression are crucial for the proper functioning of cellular and humoral immune responses, it will be most interesting to understand how the control of MHC gene expression changes with age and whether MHC gene expression can be modulated in old individuals to restore better immune function.