Immunological responses in lymph nodes of the cat.

To study the zonal response to antigenic stimuli in lymph nodes of the cat, three groups of eight cats received epicutaneous application of oxazolone and inoculations of ovalbumin plus Freund's adjuvant and feline leukaemia virus (FeLV) respectively into the left hind footpads. The changes in the left popliteal nodes were followed histologically and autoradiographically for 14 days. In the oxazolone-treated group, there was an extremely marked proliferation of blast cells in the paracortical areas, maximal on days 3–7; germinal centres developed on day 6; plasma cells did not feature in the response. In the ovalbumin-treated group, the nodes developed a full zonal response, with marked blast cell response in the paracortical areas, formation of prominent germinal centres and a striking plasma cell reaction. In both groups, there was a considerable increase in mast cell numbers in the course of the reactions; the origin of the new mast cells was not clear. The response to FeLV was minimal, despite direct stimulation of the node with high titre virus.