Monocytic origin of human alveolar macrophages.

The monocytic lysosomal acid esterase (AcE; EC 3.1.1.6) comprises five isoenzymes, each having specific isoelectric points (pI) as well as antigenicity. In the present study attempts were made to retrace the monocytic origin of human alveolar macrophages (AM) by comparison of their isoenzyme patterns with those of blood monocytes. Resident AM obtained from bronchial lavages lacking any neutrophils and unstimulated monocyte admixture showed in addition to the five monocytic isoenzymes nine additional isoenzyme loci. In vitro stimulation of blood monocytes (BM) using lymphokine-conditioned media led to a gradual transition of the typical monocytic isoenzyme pattern into that of AM. It is concluded that AM originates from blood monocytes by tissue-specific stimulation. This cellular transformation can be modeled in vitro as far as morphology, cytochemistry, and isoenzyme pattern are concerned.