Heterogeneity among alveolar macrophages in humoral and cell-mediated immune responses: separation of functional subpopulations by density gradient centrifugation on Percoll.

Rabbit alveolar macrophages (AM) were separated into four subpopulations by centrifugation on discontinuous density gradients of Percoll. The subpopulations were compared to unseparated AM populations for their ability to provide accessory function to adherent cell-depleted splenocytes for antigen-stimulated lymphoproliferation and for the production of lymphokine. They were also tested for their ability to modulate in vitro plaque-forming (PFC) responses. AM subpopulations that provided accessory function for the production of migration inhibitory factor (MIF)-containing culture supernatants were recovered from the least dense fractions of the Percoll gradients. These cells were cytochemically characterized as mature cells. AM that suppressed the in vitro PFC response and augmented the antigen-stimulated lymphoproliferative response to the greatest degree were recovered from the most dense fractions of the Percoll gradients and were characterized as immature cells. These results suggest that there are distinct subpopulations of AM, the function of which may represent different stages of maturation (or differentiation).