Control of Leishmania major Infection in BALB/c Mice by Inhibition of Early Lymphocyte Entry into Peripheral Lymph Nodes 1

A single i.p. injection with the anti-CD62L (anti-L-selectin) mAb Mel-14 before parasite challenge protected BALB/c mice from the otherwise lethal infection with Leishmania major. The Mel-14 mAb treatment resulted in a significant (>90%) decrease in cellularity of the popliteal lymph node (PLN) with a decrease in the proportion of CD4⁺ cells and an increase of the proportion of B220⁺ cells. Furthermore, both activated cells (CD25⁺ and CD69⁺) and cells of the memory phenotype (CD45RB^dull CD44^high) were significantly enriched in PLN from Mel-14-treated BALB/c mice. After infection with L. major, the otherwise massive cellular infiltration in the draining PLN was completely blocked in the Mel-14-treated mice, and in these animals the high representation of both activated and memory cells in PLN remained characteristic for the first days of infection. The protective effect was found to be associated with a markedly increased production of IFN-γ and with a decrease in IL-4 production upon restimulation of PLN and spleen cells with L. major Ag in vitro. The cured mice were found to be resistant against a secondary challenge with the parasites. These data suggest that the induction of a nonprotective Th2 response to L. major is associated with the entry of lymphocytes from the recirculating pool into the draining LN. The Mel-14-induced changes in the lymphoid microenvironment of the draining peripheral LN appear to favor the development of a protective Th1 cell-mediated immune response against the parasite.