Evaluation of the structural and functional changes in the lymphoid organs of Boran cattle infected with Trypanosoma vivax.

Experimental infection of Boran cattle with Trypanosoma vivax resulted in fluctuating parasitemia detectable in peripheral blood which, as the infection progressed, diminished to undetectable levels. In animals necropsied during the initial stages of the infection, trypanosomes were detected in lymph and in the sinuses of the lymph nodes. The lymph nodes and spleen exhibited marked proliferative response which was maximal in animals killed on days 10 and 17 of infection. The response was characterized by an increase in the size and activity of the germinal centers accompanied by increased numbers of large proliferating lymphocytes in the medullary cords and peripheral part of the paracortex of the lymph nodes and in the periarteriolar regions and peripheral follicular areas of the spleen. This was associated with the production of large numbers of plasma cells which were present in the red pulp of the spleen, in the medullary cords of the lymph nodes, and focally in the peripheral paracortical areas of the lymph nodes. By immunofluorescence, many of these plasma cells were found to contain immunoglobulin (Ig) M. There was also increased number of follicles which exhibited granular deposits of IgM and reduction in the areas containing small lymphocytes bearing IgM. During the remainder of the infection and paralleling the decrease in parasitemia, there was gradual reduction in the reactivity of the lymphoid organs. Accompanying the initial proliferative response was a marked increase in plasma concentration of IgM; this decreased to base line during the 3rd week of the infection. The response to phytohemagglutinin, pokeweed mitogen, and lipopolysaccharide of leukocytes obtained from peripheral blood lymph nodes and spleen at intervals during the infection was not significantly different from controls.