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Intestinal lymph-duct cannulae were established in normal and mesenteric lymphadenectomized (MLNx) pigs for the 6-day duration of a local intestinal immune response to a protein antigen (ovalbumin). The daily output of anti-ovalbumin-containing cells (AOCC) in intestinal lymph and the numbers of AOCC in the intestinal lamina propria at the end of the experiment were recorded. Very few AOCC were recovered in the intestinal lymph of normal pigs whereas in MLNx pigs large numbers were recovered reaching a peak output on day 4. However, there were significantly more AOCC detected in the jejunal lamina propria of normal pigs than MLNx pigs despite continuous drainage of intestinal lymph throughout the response. The absence of AOCC from efferent intestinal lymph of normal pigs, the failure of chronic intestinal-lymph drainage to abrogate the AOCC response in the intestine of these pigs and the reversal of these findings in MLNx pigs indicate that, in contrast to other species, lymphoblasts are diverted from porcine intestinal lymph, and probably enter the blood circulation at the level of the mesenteric lymph node (MLN).

Evidence is presented which indicates that recirculating lymphocytes originating from the intestine in pigs are returned to the blood circulation at the level of the mesenteric lymph nodes (MLN) and not via efferent intestinal lymph. This was demonstrated by three observations: (1) removal of all MLN resulted in a thirty-fold increase in lymphocyte numbers in efferent lymph of pigs, but not in rats; (2) there are about twenty-five times more lymphocytes in afferent intestinal lymph than efferent intestinal lymph in normal pigs; (3) 51Cr-labelled lymphocytes injected into afferent lymphatics are mostly recovered in the node tissue or efferent lymph of sheep, and very few in the venous drainage, whereas in pigs relatively few labelled cells are recovered in the node or in efferent lymph.