Leukocyte adherence inhibition (LAI) in rats bearing transplantable syngeneic tumors of different immunogenicity.

The tube leukocyte adherence inhibition (LAI) assay was used to follow the LAI response in inbred BN rats with subcutaneously (s.c.) transplanted syngeneic liposarcoma (LS175) tumor and in inbred WAG rats with s.c. transplanted syngeneic colon (CC531) and skin (1618) tumors. Initially, the tube LAI assay was used to follow the LAI reactivity of peripheral blood leukocytes (PBL) from BN rats bearing tumor LS175. Sporadic LAI reactivity was observed in the PBL of these rats when incubated with a specific crude tumor extract for either 2 or 20 hr. No definite conclusion regarding the lack of significant tumor-specific LAI reactivity could be drawn since LS175 is a non-immunogenic tumor. Therefore additional LAI studies were performed with the weakly immunogenic tumor CC531 and the highly immunogenic tumor 1618 in WAG rats. Surprisingly, only sporadic LAI reactivity was observed in the PBL of rats bearing either the CC531 or the 1618 tumors using both the 2 and 20 hr LAI assays. This absence of tumor-specific LAI reactivity was particularly remarkable in the highly immunogenic 1618 tumor-bearing rats, since it would suggest that the antigen(s) responsible for its high immunogenicity could not evoke any consistent LAI reactivity. Since oxidative metabolites of arachidonic acid have been shown to be the final mediators of chemoattractant-induced LAI, the adherence inhibition effect of leukotriene B4 (LTB4) on the PBL of BN and WAG rats was also investigated in order to exclude the possibility that the lack of consistent LAI reactivity was due to a lack of responsive cell population in the PBL. PBL of both BN and WAG rats showed a significant increase in the adherence inhibition in the presence of LTB4, suggesting that the sporadic LAI reactivity was not due to a lack of responsive cell population.