Immunobiological Studies on Experimental Visceral Leishmaniasis IV. Kinetics of Evolution of Disease-Promoting Versus Host-Protective Cells of Monocyte-Macrophage Lineage and their Characterization


Dr Syamal Roy, Department of Immunology, Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Calcutta, 700 032, India


The evolution of cells of the monocyte-macropbage lineage (MML cells) in the spleen of Leishmania donovani (LD) infected BALB/c mice was studied. Spleen cells were fractionated on a discontinuous percoll gradient and adherent cells (AC) were purified from fractionated spleen cells by adherence steps that appeared at the interfaces of 25–35%, 35–40%, 40–45% and 45–50% percoll gradients. The AC were characterized as MML cells on the basis of positive staining for non-specific esterase. Adherent cells that appeared at the interfaces of 25–35% and 40–45% were defined as A and C, respectively, and both of them showed extreme variation in a progressive infection. It was observed that A supported parasite replication whereas C remained refractory when infected with LD in vitro. Furthermore, when A cells and C cells were used as antigen-presenting cells to stimulate mixed population of IFN-γ producing and IL-4 producing T-cells, it was observed that IL-4 and IFN-γ were the predominating cytokine in the T-cell supernatant, respectively. Both A and C were found to be increased hand-in-hand up to 5 months of infection and from then on A decreased and C increased in their numerical strength (A-C reciprocity). The evolution of A-C reciprocity coincided with the gradual reduction in the parasitaemia in the spleen suggesting that this may contribute to the acquisition of anti-leishmania immunity.