Evidence that retrovirus expression in mouse spleen cells results from B cell differentiation

Induction of endogenous retroviral proteins from spleen cells exposed to lipopolysaccharide (LPS) was studied in individual cells in relation to polyclonal B cell differentiation. After 4 days of culture with LPS, 30 to 40% of cells in many mouse strains stained for cytoplasmic mu heavy chains. A smaller number of lymphoid cells stained for cytoplasmic viral proteins, with a characteristic proportion for each strain, including 21% of lymphoid cells of AKR mice, 125 of DBA/2 cells, 7% of C57BL/6 cells, and 2% of BALB/c cells. More than 75% of retrovirus-positive cells were also mu-chain-positive in all strains. Cells from young (3- to 8-week-old) and old (43- to 46-week-old) mice of several strains showed similar proportions of retrovirus-positive cells typical for each strain, without differences at different ages. The induction of retrovirus proteins, as well as mu-chains, by LPS was markedly inhibited by goat anti-mu-chain antibody added to the culture medium (10 to 100 micrograms/ml). These data suggest that retrovirus induction may result from B cell differentiation.