Oxidative responses of rabbit alveolar macrophages: comparative priming activities of MIF/MAF, sera, and serum components.

The comparative abilities of various reagents to prime rabbit alveolar macrophages (AM) to produce reactive oxygen intermediates (ROI) in a chemiluminescent (CL) assay were investigated. It was noted that AM from normal rabbits cultured in a serum-free medium for 18 hr exhibited a "spontaneous" priming response following a challenge with phorbol myristate acetate (PMA); however, "spontaneous" priming was not evident when the AM were cultured for only 3 hr. It was further established that pretreatment of normal AM for 3 or 18 hr with MIF/MAF preparations (serum-free), fetal bovine serum (FBS), or bovine serum albumin (BSA) exhibited marked increases in their CL responses following challenge with PMA. When FBS was used in the culture medium, the priming activity of MIF/MAF was masked because of the high CL responses of controls due to the priming effects of FBS. BSA at concentrations approximately equivalent to the amount in FBS also displayed marked priming activity. Bacterial products (lipopolysaccharide and muramyl dipeptide), latex particles, rabbit IgG, PMA, and opsonized as well as nonopsonized zymosan and bacteria (BCG and Staphylococcus epidermidis) were inactive as priming agents. In comparison, AM from BCG-immune rabbits that were primed in vivo yielded a very large CL response when challenged with PMA. Opsonized zymosan and bacteria produced twofold increases in the CL responses in BCG-immune AM compared to nonopsonized preparations. The marked priming effect of serum on AM cultured for even a short period (3 hr) indicates that normal AM undergo marked changes in culture that complicate the interpretation of AM function when AM are cultured in vitro in media containing serum.