Blocking factor in sera of MC1 and B77 tumor bearing rats detected by LAI assay.

A modified form of the leukocyte adherence inhibition assay (LAI assay) has been used to detect the blocking factor in serum of the Lewis (LW) inbred rats and the F1 hybrids of the inbred LW X AVN strains with transplantated syngeneic B77 and MC1 tumors. This study has indicated that the cell mediated antitumor immune response of rats immunized with living tumor cells and the blocking factor in serum of rats with progressively growing tumors may be demonstrated by the LAI assay with incubation time prolonged to 20 hr (LAI assay-IT20). In addition, the specificity of the blocking effect and the disappearance of blocking factor after surgical removal of tumors have also been demonstrated in this paper.