Effect of Irradiation and Appendicostomy on Appendix Structure and Responses of Appendix Cells to Mitogens

Abstract

Abstract A quantitative morphologic analysis was made of changes in the appendix nodule in rabbits receiving sublethal whole body irradiation and in others after ligation of the base of the appendix, appendicostomy and sterilization of the appendix lumen. After 450 r, the dome, the thymus-dependent area (TDA), and the follicle (thymus-independent area) all decreased rapidly in size to a minimal value at 7 days, and then began to regenerate. The follicle shrank more rapidly and to a greater extent than the TDA. After appendicostomy, the dome maintained its volume for 10 days, then slowly decreased in size. The TDA and follicle began to shrink immediately and in parallel, diminishing by 10 to 14 days to a size comparable to that in irradiated rabbits. If irradiation were superimposed on appendicostomy, these tissue elements diminished still further. The dome showed partial regeneration. These data support the hypothesis that the dome may serve as a mammalian bursa-equivalent (B) and that both TDA and B cell areas depend for their proliferative stimulus on microorganisms or other materials coming from the lumen. When cultured 7 days after irradiation, cells of the appendix, sacculus rotundus, and draining mesenteric lymph node (but not the Peyer's patches or spleen) showed an elevation in response to Phytohemagglutinin (PHA), presumably reflecting a relative decrease in B cells and increase in radioresistant T cells. This had largely disappeared by 14 days. After appendicostomy and lumen sterilization, the PHA response of appendix cells began to increase at 7 days together with that of cells from the mesenteric node, and became quite elevated at 14 days, while cells of the sacculus, Peyer's patches and spleen showed no change. After appendicostomy and irradiation, the response of appendix cells to PHA remained relatively elevated. Concanavalin A (ConA) responses in general paralleled response to PHA. Cells of the gut-associated lymphoid organs showed a much lower ratio of responses to ConA and PHA than did lymph node cells, and this ratio was less than 1.0 in the acute phase (3 and 7 days) of irradiation injury. Endotoxin produced little stimulation at any time.