Development of fish peritoneal macrophages as a model for higher vertebrates in immunotoxicological studies: I. Characterization of trout macrophage morphological, functional, and biochemical properties

Abstract The immune defense mechanisms of fish are not as well characterized as those of mammals but seem to be related and similarly competent. Because of this, there is an increased interest in the immune responses of fish as models for higher vertebrates in immunotoxicological studies. Prior to such studies, baseline criteria for specific components of the immune response needed to be established. For this study, we have examined trout macrophage morphology using light and scanning electron microscopy, phagocytic activity, random and stimulus-directed migration, and superoxide anion radical ( • O 2 − ) production for resident and lipopolysacharide (LPS) or Aeromonas salmonicidae -elicited rainbow trout ( Oncorhynchus mykiss ) peritoneal macrophages (Mφ). Following peritoneal lavage, >89% of the cells were Mφ as determined by differential counts and nonspecific esterase staining. Immunization with LPS and A. salmonicidae increased Mφ number ∼5 and 13-fold, respectively, and overall size. Trout Mφ were phagocytically active engulfing serum opsonized latex particles and were mobile, migrating both randomly and in a directed fashion towards formyl-methionine- l -leucine- l -phenylalanine (FMLP) and trout serum-derived complement fragment C5a. Concentrations of FMLP (100 n m ) and C5a (0.01−1%) effective for attracting trout Mφ are the same as those used to attract rabbit Mφ. Resident trout Mφ produced negligable quantities of • O 2 − following stimulation with 1 μg/ml phorbol myristate acetate; Aeromonas -elicited Mφ produced • O 2 − in a time-dependent manner which peaked after 60 min at 2.9 nmol per 2 × 10 5 cells and then declined. The results of this study provide a data base for future toxicological studies with trout peritoneal Mφ and indicate the usefulness of this system for immunotoxicological studies.