Journal of Experimental Medicine, Vol 144, 920-932, Copyright © 1976 by Rockefeller University Press
Normal rabbit alveolar macrophages. II. Their primary and secondary lysosomes as revealed by electron microscopy and cytochemistry
BA Nichols
In this investigation, vacuoles containing tubular myelin proved to be
digestive compartments with cytochemical reactivity for acid phosphatase
and arylsulfatase. These cytochemical markers identify the secondary
lysosomes, known to contain enzymes capable of hydrolyzing phospholipids
like surfactant. Therefore, it appears that alveolar macrophages possess
the enzymatic machinery for the degradation of the tubular myelin found in
their digestive vacuoles. Although it thus appears evident that alveolar
macrophages participate in the turnover of surfactant, the quantitative
significance of this route of disposal is undetermined. This investigation
has also established that acid hydrolases, so prominently displayed in the
secondary lysosomes, are also localized in the rough endoplasmic reticulum
and in Golgi- endoplasmic reticulum-lysosomes (GERL). Moreover, small
vesicles which are produced from GERL serve as primary lysosomes in
transporting digestive enzymes to the vacuoles.