Abstract
An antigen‐stimulated active rosette assay was adapted as an in vitro assay for the detection of lymphocyte reactivity to soluble tumor extracts. The specificity of this assay was demonstrated with lymphocytes from non‐sensitized swine and swine sensitized to either mammalian tuberculin or DNCB‐bovine serum albumin conjugates (DNCB‐BSA). An increase in active rosette‐forming cells (A‐RFC) occurred only when sensitized lymphocytes were stimulated with specific sensitizing antigen. Lymphocytes from melanoma swine reacted in vitro to 3 M KCl extracts of autologous and allogeneic melanomas but did not react to 3 M KCl extracts of autologous and allogeneic swine skin. Lymphocytes from 33 melanoma swine and 17 normal swine were tested for in vitro reactivity to an allogeneic melanoma extract; 84.8% of the melanoma swine demonstrated lymphocyte reactivity to allogeneic melanoma extract and 23.5% of the normal swine reacted positively to allogeneic melanoma extract. The reactivity of melanoma swine lymphocytes to allogeneic melanoma extract was not due to reactivity of the lymphocytes to normal skin antigens or fetal swine antigens present in melanoma extracts; normal and melanoma swine lymphocytes demonstrated only low in vitro reactivity to 3 M KCl extracts of normal swine skin and fetal swine tissue. Lymphocytes from three melanoma swine increased in A‐RFC after incubation with each of nine allogeneic melanoma extracts, indicating that the ability to stimulate lymphocyte reactivity was not limited to a single allogeneic melanoma extract. The results of this study indicate that a tumor‐related immune response occurs in melanoma swine and that in vitro lymphocyte reactivity is directed towards a tumor‐associated antigen or tumor‐associated antigen‐like substance present in 3 M KCl extracts of swine melanoma.