Attachment and phagocytosis by salmon macrophages of agarose beads coated with human C3b and C3bi.

Agarose beads (diameter 5-10 micron) preincubated in human serum became associated (attached and ingested) to 50-60% of the salmon macrophages within 60 minutes. However, Beads preincubated in serum treated with heating (50 degrees C, 20 min) or with EDTA (10 mM) to inhibit the activation of alternative complement pathway, were not associated to the phagocytes. Furthermore, agarose beads coated with human C3b and C3bi after incubation with isolated complement factors (C3, D, B), were associated to 30-40% of the phagocytes. About 80% of the cell-associated agarose beads was intracellularly located. Conversion by trypsin treatment (0.01%) of agarose bound C3bi to C3d, abolished the association of such beads to the macrophages. The results demonstrate that salmon macrophages possess complement receptors that bind human C3b and C3bi. Agarose beads coated with these ligands (C3b and C3bi) are attached and ingested by the phagocytes.