Induction of homotypic aggregation in the rainbow trout macrophage-like cell line, RTS11

The rainbow trout monocyte/macrophage-like cell line, RTS11, has been used to study homotypic aggregation (HA), which is a well-studied feature of leucocytes in mammals but less understood in fish. HA is the aggregation of cells of the same cell type. RTS11 underwent HA in response to polyinosinic:cytidylic acid (poly IC), polyadenylic acid (poly A), lipopolysaccharide (LPS), zymosan, and phorbol 12-myristate 13-acetate (PMA). Poly IC was the best inducer of HA and did so in a dose- and time-dependent manner. The induction of RTS11 aggregation by poly IC required divalent cations but was not blocked by either an inhibitor of lymphocyte function-associated molecule-1 (LFA-1) or the tripeptide integrin adhesion recognition sequence, RGD. Poly IC-induced HA was inhibited by colchicine and latrunculin B, which act on microtubules and microfilaments, respectively, implying the necessity for an intact cytoskeleton. HA induction by poly IC did not occur at 4 degrees C and was blocked by the transcriptional and translational inhibitors, actinomycin D and cycloheximide, respectively, suggesting the requirement for de novo protein synthesis. Poly IC-induced RTS11 aggregation was blocked by two inhibitors of dsRNA-dependent protein kinase (PKR). This is the first indication that PKR could have a role in the HA of leucocytes.