Vasoactive intestinal polypeptide (VIP) inhibits rat alveolar macrophage phagocytosis and chemotaxis in vitro

Vasoactive intestinal polypeptide (VIP) has been shown to inhibit lymphocyte function and is believed to modulate the immune response. We explored the possible immunomodulatory effects of VIP on alveolar macrophage (AM) function by examining its influence on AM phagocytosis and chemotaxis. Rat AMs were collected by bronchoalveolar lavage and incubated for 90 min with polystyrene beads in the presence or absence of VIP in concentrations from 10(-11) M to 10(-5) M. VIP significantly (P less than 0.0001) inhibited AM phagocytosis of polystyrene beads at concentrations of 10(-11) to 10(-6) M, with a maximal inhibition of 35% at 10(-6) M (but no inhibition at 10(-5) M). AMs were also incubated for 90 min in a chemotaxis chamber with endotoxin-activated rat serum (EARS) as a chemoattractant, with or without VIP in concentrations from 10(-9) to 10(-6) M. VIP significantly (P less than 0.0001) inhibited AM chemotaxis by at least 30% at concentrations of 10(-9) to 10(-6) M, with a maximal inhibition of 46% at 10(-7) M. These results indicate that VIP, in concentrations from 10(-11) to 10(-6) M, inhibits rat AM function as assessed by phagocytosis of polystyrene beads and chemotaxis to EARS. The inhibition of alveolar macrophage function is another mechanism by which VIP may modulate the immune response in the lung.