β₂-lntegrin dependent aggregate formation between LB T cell lymphoma and spleen cells: Assessment of correlation with spleen invasiveness

LB is an aggressive T cell lymphoma which rapidly invades the spleen and lymph nodes of BALB/c mice after s.c. inoculation. We previously reported that mAb directed against the β₂ chain of the leukocyte function-associated antlgen-1 (LFA-1) adhesion molecule (CD18) blocked the invasion of LB cells into the spleen but not into the lymph nodes. The same antibody also blocked in vitro aggregate formation between normal spleen cells and LB cells. However, aggregate formation between normal lymph node cells and LB cells was not detected, regardless of ratio. In an attempt to evaluate the association between aggregate formation and tumor invasion of the lymphold organs, we have now extended the study. Intravenous injection of anti-CD18 mAb, which blocked spleen invasion by LB cells, also blocked the formation of ex vivo aggregates, spontaneously generated in spleen, but not in lymph node, cell suspensions of BALB/c mice s.c. Inoculated with LB cells. In contrast, mAbs unable to block spleen invasion were ineffective inhibitors of both in vitro and ex vivo aggregate formation between spleen and LB cells. Spleens of nude mice that did not provide a supportive environment for lymphoma invasion, were also deficient in target cells forming aggregates with LB cells. In line with this observation, enriched T cells formed more aggregates with LB cells than did enriched non-T cells, Indicating the lymphoma's preferential binding to splenic T cells. Aggregate-borne LB cells and LB cells which were not included in aggregates, Invaded the spleen and the lymph nodes to the same extent. However, non-aggregated LB cells acquired the ability to form aggregates after 1 week of in vitro cultivation, suggesting that this capacity may also be acquired in vivo. Antl-CD44 mAb, in distinct contrast to antl-CD18 mAb, blocked LB cell invasion of the lymph node, but not of the spleen. However, when antl-CD44 mAb was co-Injected with antl-CD18 mAb it antagonized the blocking effect of antl-CD18 mAb on spleen invasion and formation of ex vivo splenic aggregates. The interpretation of these results in conjunction with the association between splenic aggregate formation and spleen invasion by LB cells is discussed.