Lag-3 Expression And Its Role During Mycobacterium Tuberculosis Infection In Non-human Primates
Mycobacterium tuberculosis (Mtb) is the causative agent of the disease tuberculosis (TB). While approximately one third of the world's population is infected with this pathogen, only a small minority of these individuals has active TB infection, where these individuals are able to transmit the pathogen to others. In previous microarrays performed in our lab from lung tissue of non-human primates (NHPs), it was noted that animals undergoing the activation of TB showed greatly increased expression of lymphocyte activation gene 3 (LAG-3). This protein performs immunomodulatory roles, which include: increased function of regulatory T cells, decreased function of Th1 effector T cells, and decreased monocyte differentiation. When studied in rhesus macaques infected with Mtb, RNA expression and protein levels of LAG-3 in lung tissue of active TB animals was found to be greatly increased when compared to lung from animals with latent TB. Interestingly enough, there was a bimodal distribution of LAG-3 expression in animals undergoing reactivation of the disease; the animals with greater levels of LAG-3 were the fast reactivators. LAG-3 expression in the lung tissue of animals with Mtb infections was mainly isolated to the outer periphery of the Mtb induced lung granuloma, where predictably, LAG-3 was expressed by lymphocyte populations of immune cells; mainly NK cells and various populations of T cells. To gain a greater understanding of the function of LAG-3, we created a co-culture system where CD4 T cells derived from blood and lung of Mtb infected NHPs were supplemented to Mtb infected differentiated monocytes. With this co-culture model, we utilized short interfering RNA (siRNA) to silence LAG-3. We observed a decreased bacterial burden, as well as decreased frequencies of IL-10 and IFN-Î³ producing CD4 T cells. This illustrates that the silencing of LAG-3 in CD4 T cells resulted in increased bacterial clearance, not due to up-regulation of IFN-Î³. We believe that the bacterial reduction may be due to increased T cell proliferation, along with production of another proinflammatory cytokines. In the near future, we will utilize cytokine assays and microarrays to better understand the mechanism of action through which increased bacterial killing is occurring.