GENETIC-RESISTANCE SUSCEPTIBILITY TO MYCOBACTERIA - PHENOTYPIC-EXPRESSION IN BONE-MARROW DERIVED MACROPHAGE LINES

Congenic strains of mice susceptible (B10A.Bcg(s)) or resistant (B10A.Bcg(r)) to BCG were established. Here we describe the model system which has been established to analyze the functional activities of macrophages in the two strains. We have immortalized bone marrow macrophages from B10A.Bcg(s) and B10A.Bcg(r) congenic strains of mice and derived cloned macrophage lines designated B10S and B10R, respectively. B10R and B10S cell lines exhibited surface markers and morphology typical of macrophages. B10S and B10R were similar in their phagocytic activity, in their level of c-fms, in their transforming growth factor-beta (TGF-beta) mRNAs expression, and in their expression of tumoricidal activity in response to interferon-gamma (IFN-gamma) plus lipopolysaccharides (LPS). However, B10R macrophages expressed a higher level of Ia mRNA when activated with IFN-gamma compared with B10S macrophages. Analysis of the bacteriostatic activity of the two cell lines revealed that B10R macrophages were much more active in inhibiting Mycobacterium smegmatis replication than B10S. To measure the intracellular destruction of bacilli, a bactericidal assay based on hybridization with an oligonucleotide probe specific for mycobacterial ribosomal RNA was designed. The results demonstrated that B10R macrophages were endowed with enhanced constitutive bactericidal activity as compared with B10S. In conclusion we have obtained macrophage lines from bone marrow of B10A.Bcg(s) and B10A.Bcg(r) mice that express to a similar extent functional and phenotypic characteristics of macrophages. However, we demonstrate that relative to B10S macrophages, the B10R macrophages have higher expression of Ia mRNA and that they are constitutively more active in expressing mycobactericidal activity.