LIPOPOLYSACCHARIDE-STIMULATED EVENTS IN B-CELL ACTIVATION

High concentrations of thymus-independent (TI) antigens are capable of inducing polyclonal B cell activation by their intrinsic mitogenic pr operties, irrespective of the specificity of the Ig receptors. Due to a genetic defect on the 4th chromosome, B cells from C3H/HeJ mice do n ot respond to lipopolysaccharide (LPS). In order to define at which st ep the mutation affects the signalling pathway, we compared B cells fr om C3H/HeJ and CBA mice with regard to changes of three events, namely cell size, and MHC class I and II antigen expression after LPS stimul ation. We found that cell size and expression of MHC antigens increase in B cells from CBA mice after LPS stimulation, whereas B cells from C3H/HeJ mice do not respond at all. This suggests that the defect in C 3H/HeJ mice interferes with early events in the signalling pathway, ei ther due to the absence of a LPS receptor on B cell surface or the lac k of an initial component necessary for effective signal transmission subsequent to LPS receptor binding. Our results also have shown that s timulation of anti-Ig antibodies and LPS differ in some signalling eve nts and have different final effects on B cells, which suggests that t hey may function differently via distinct signalling pathways.