Trichinella spiralis: changes caused in the mouse's thymic, splenic, and lymph node cell populations.

Infections with the nematode Trichinella spiralis induce unresponsiveness in mice. A study was made to determine whether suppression could be due to a deficiency in the cells responsible for the immunological response. Mice were given low or moderate infections and were killed 7, 14, 28, or 56 days after inoculation; spleen macrophages and leucocytes, θ cells, and Con A- and LPS-sensitive cells were determined in the thymus, spleen, and the mesenteric and axillary lymph nodes. Spleen macrophages are diminished throughout the course of the infection, reaching significantly low levels on the 14th day. The thymus loses, whereas the spleen and the axillary node gain, cells bearing the θ antigen. In spite of the increase in leucocytes and θ cells in the secondary lymphoid tissue, the cells of these organs are insensitive to the blastogenic action of Con A in the heavier infections. In lower infections, however, spleen cells show an enhanced response to Con A and LPS; mesenteric cells, on the other hand, show an early enhanced susceptibility to LPS and a reduced susceptibility to Con A and, in the later phases of parasitism, an enhanced Con A and a reduced LPS susceptibility. It is suggested that these phenomena contribute to the immunosuppression phenomena which are characteristic of T. spiralis infections.