Effects of Tumor Necrosis Factor Alpha on Dendritic Cell Accumulation in Lymph Nodes Draining the Immunization Site and the Impact on the Anticryptococcal Cell-Mediated Immune Response

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Abstract
Cell-mediated immune (CMI) responses and tumor necrosis factor alpha (TNF-α) have been shown to be essential in acquired protection againstCryptococcus neoformans. Induction of a protective anticryptococcal CMI response includes increases in dendritic cells (DC) and activated CD4+T cells in draining lymph nodes (DLN). During the expression phase, activated CD4+T cells accumulate at a peripheral site where cryptococcal antigen is injected, resulting in a classical delayed-type hypersensitivity (DTH) reaction. Induction of a nonprotective anticryptococcal CMI response results in no significant increases in the numbers of DC or activated CD4+T cells in DLN. This study focuses on examining the role of TNF-α in induction of protective and nonprotective anticryptococcal CMI responses. We found that neutralization of TNF-α at the time of immunization with the protective immunogen (i) reduces the numbers of Langerhans cells, myeloid and lymphoid DC, and activated CD4+T cells in DLN and (ii) diminishes the total numbers of cells, the numbers of activated CD4+T cells, and amount of gamma interferon at the DTH reaction site. Although TNF-α neutralization during induction of the nonprotective CMI response had little effect on cellular and cytokine parameters measured, it did cause a reduction in footpad swelling when mice received challenge in the footpad. Our findings show that TNF-α functions during induction of the protective CMI response by influencing the accumulation of all three DC subsets into DLN. Without antigen stimulated DC in DLN, activated CD4+T cells are not induced and thus not available for the expression phase of the CMI response.

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