THE IN-VIVO ANTIBODY-RESPONSE AGAINST EXOGENOUS ANTIGENS IS NOT INFLUENCED BY THE MOUSE BCG (NRAMP1) GENE

The mouse Nramp1 (Bcg) gene on chromosome 1 exerts pleiotropic effects on macrophage function. The gene is known to affect presentation of m ycobacteria, and other antigens in vitro, so that macrophages carrying the resistant Bcg allele better support the proliferation of antigen- specific T cells compared with macrophages of the sensitive phenotype. To determine whether the Bcg allele could affect in vivo the antibody response to antigens not related to mycobacterial infections, we test ed the primary and secondary responses to sheep red blood cells (SRBC) and glycosylated bovine insulin (G-insulin) in two pairs of Bcg conge nic strains: BALB/c (Bcg(5)) versus BALB/c.CD2 (Bcg(s)), and B10.A (Bc g(s)) versus B10A(r) (Bcg(s)), and in C57BL/10ScSn (B10; Bcg(s)) and A /J (Bcg(r)) mice. Furthermore, the antigen-specific proliferative resp onses of T cells primed in vivo by protein antigens were also tested i n Bcg congenic mice. We found no significant difference in in vivo ant ibody response either to SRBC or G-insulin between the Bcg(r) and Bcg( s) strains. The magnitude of in vitro antigen-specific proliferation o f lymph node cells sensitized in vivo by hen egg lysozyme (HEL) or chi cken ovalbumin (OVA) was also similar in Bcg(r) and Bcg(s) congenic mi ce. However, we have documented a higher antigen-presenting capacity o f Bcg(r) macrophages in in vitro antigen-specific proliferation to OVA . Since the macrophages are the only cells in which the Nramp1 gene is expressed, we suggest that the activity of other types of antigen-pre senting cells masks the effect of the Bcg(r) allele on antigen-present ation in vivo.