Concomitant immunity against Sarcoma E 100 comparing 2 strains of rats

: Concomitant immunity (IC) is usually defined as the capacity of any animal bearing a progressor tumor to inhibit a second challenge with the same tumor. In order to establish the contribution of the host to the origin of this phenomenon, IC was induced in two lines of rats with a different behavior when challenged with Sarcoma E 100 (SE 100), i.e., line IIMc: 90% take and 100% regression; line "m": 100% take and death. The rats received a second challenge on day 3 (Group II), 7 (III), and 14 (IV), as well as the control groups: II', III' and IV', respectively. The animals reinoculated on day 7 showed a decrease, both in percentage of takes (Fig. 1, III vs III') and tumor surface (Table 1, 2). Likewise, in rats IIMc, a lesser development of the first inoculum (Table 1, Ia vs I') was observed. The Winn assay (Table 3) confirmed the presence of immunocompetent spleen cells (CE) against SE 100 in IIMc rat spleens: namely, 1) immune rats (II), 2) unique tumor bearing rats (IV), 3) first progressor and second negative inoculum (V). In line "m" the percentage of takes was only smaller in the group inoculated conjointly with CE from immune rats (Table 3, VI vs VII). A mere 10% (3/30) of "m" rats were immunized against SE 100. Consequently, these results could attribute the IC, in IIMc rats, to immunological mechanisms, while in "m" it could be due to factor(s) released and/or induced by the first tumor, as proposed by Gorelik.