IMMUNE-RESPONSE OF RAT SPLEEN-CELLS TO A CARCINOGEN AND TO VACCINATION WITH ANTI-P53 POLYCLONAL ANTIBODIES

Background: The tumor-suppressive effects of rabbit anti-p53 antibodie s on chemically induced rat colon cancer were demonstrated previously (Cancer J, 10:116-120, 1997). Methods: In this communication, the sple en's role in the immune response of rats to cancer. and vaccination wa s evaluated histologically and immunohistochemically. The following gr oups of rats were studied: a) control non treated rats; b) tumor-free non vaccinated rats treated with a carcinogen; c) tumor-bearing non va ccinated rats; d) tumor-free vaccinated rats exposed to a carcinogen; e) tumor-bearing vaccinated rats. Results: Exposure to a carcinogen (g roup 2) caused the appearance of the proliferative and apoptotic chang es associated with immune response. They included abundant blast trans formation of CD20-positive B lymphocytes, expansion of germinal center s and of periarterial sheaths (CD3-positive T cells), an increase in t he number of plasma cells, mitotic and apoptotic cells in sie follicle s, and in CD25 IL2-depending T cells. The presence of colon tumors (gr oup 3) caused insufficiency of the splenic lymphoid system: blast tran sformation was weaker; the white pulp area decreased and its devastati on was reflected in fewer lymphoid cells. There were less plasma cells in the red pulp, while the number of dendritic cells, CD25+ T cells, macrophages and neutrophils increased sharply: suggesting a compensato ry reaction to the severe antigenic effects. Similar, but stronger cha nges, occurred in tumor-free vaccinated rats (group 4). In tumor-beari ng vaccinated rats (group 5), the rate of proliferation change was hig her than in group 3, probably as a result of a weaker splenic insuffic iency. A strong correlation was found between the number of mitotic, a poptotic or dendritic cells, tumorigenesis and vaccination. Conclusion s: A sharp increase in the number of dendritic cells in vaccinated tum or-bearing rats suggests that these cells participate in the host's re action to tumorigenesis. We conclude that vaccination with anti-p53 po lyclonal antibodies activates lymph components of the spleen.