Early onset of serum blocking in a murine melanoma model.

The early onset of serum blocking of host cell-mediated immunity was investigated in a transplantable murine melanoma employing two in vitro assays. One of these was based on the Takasugi and Klein cytotoxicity test; the other was a new test based on the inhibition of adherence of leukocytes to a plastic surface in the presence of tumor antigen. Both tests yielded similar results, and the adherence inhibition test was more sensitive. Blocking could be detected as early as 1 h after the inoculation of 1 times 10(7) melanoma cells. Early onset of serum blocking was also demonstrable if homogenized of tissue-cultured tumor cells were inoculated. Serum blocking under these circumstances was initially transient, declining at 24 to 48 h, but reappearing by the 4th day after inoculation. Furthermore, a functional immune system was not required for blocking factor development in this system, as evidenced by the onset of a similar pattern of blocking activity in heavily irradiated animals.