Reciprocal control of Mycobacterium avium and Mycobacterium tuberculosis infections by the alleles of the classic Class II H2-Aβ gene in mice.

Genetic control of host susceptibility to M. avium, an important lung pathogen of immune-compromised individuals, remains incompletely defined. Apart from the slc11a1 (Nramp1) gene, which plays a pivotal role in genetic control of a few intracellular pathogens, including M. avium, in mice, we know nothing about genetic loci determining susceptibility to and/or severity of M. avium-triggered disease. Previously, our lab developed a panel of H2-congenic, recombinant mouse strains for identification of the MHC genes involved in the control of M. tuberculosis infection. In the present study, we applied a few recombinant strains from this panel to study $ possible influence of allelic variations in classical Class II genes on the development of M. avium infection. Our results demonstrate a clear difference in lung pathology, post-infection survival time, lung neutrophil influx and corresponding chemokine/cytokine responses, as well as the degree of lung T lymphocyte activation, between mouse strains differing by the alleles of a single highly polymorphic Class II H2-Aβ gene. Paradoxically, mice carrying the H2-Aβb allele, which provides a notable protective effect against M. tuberculosis compared to the H2-Aβj allele, were more susceptible to M. avium infection as indicated by several parameters of the disease. We discuss possible reasons for such a reciprocal expression of phenotypes determined by a single allelic variant during two "similar" infections that may concern differences in virulence, NO-sensitivity, intracellular life style and antigenic composition between these two mycobacterial species.