Induction of the H-2 D antigen during B cell activation

Mitogenic activation causes increased expression of class I Ag of the MHC in mouse B cells. The increased expression was seen in flow cytometry analysis for both K and D in k as well as d haplotypes. A more detailed molecular analysis was carried out for H-2Dd. Increased expression (10- to 20-fold) of the H-2 Dd gene was detected at both protein and messenger RNA levels, and the time course for the accumulation of H-2 Dd protein on the cell surface parallels the increase in the steady-state messenger RNA levels. The increase in H-2 Dd expression in small B cells stimulated with LPS is detectable after 10 h of culture. The present data provide molecular and serologic evidence about alterations in the expression of the H-2 Dd Ag, previously identified as a B cell activation antigen B7.2. Our results indicate a new significance for the function and regulation of the MHC during immune responses, and suggest that the class I molecules may serve some role in the B cell activation process.