This paper describes functional and genetic studies on the macrophage resistance gene Lsh/Ity/Bcg first described almost two decades ago. Working in vitro with resident peritoneal, liver (Kupffer cells) and bone marrow derived macrophages from congenic B10 (Lsh(S)) and B10. L-Lsh(R) Mice it has been possible to demonstrate that the final effector mechanism for the gene in regulating antileishmanial activity involves production of reactive nitrogen rather than reactive oxygen intermediates. This in turn is dependent upon priming/activation of macrophages for enhanced TNF-alpha release which acts back on the macrophage in an autocrine manner to increase nitric oxide production. The precise point at which Lsh acts to control macrophage priming/activation has not been identified, but studies of early response gene expression show differences in KC mRNA levels at 2 h after LPS stimulation, and in c-fos mRNA as early as 20 min after stimulation with PMA plus ionophore, in peritoneal macrophages from congenic Lsh(S) and Lsh(R) mice. Data available suggest that both negative and positive signals may be involved in macrophage priming/activation, with Lsh(S) macrophages down-regulating their capacity for continued response to the autocrine loop. Work in progress will examine the role of TPA and cAMP response element-binding proteins in regulating gene expression in Lsh congenic mice. A major new initiative has also commenced to clone the Lsh gene by reverse genetics using yeast artificial chromosomes to walk towards Lsh from the closest proximal and distal markers on mouse chromosome 1. Family linkage analysis using restriction fragment length polymorphisms for marker genes on human chromosome 2q has begun to provide some evidence that a human homologue for Lsh may regulate resistance and susceptibility to leprosy and tuberculosis in man.
