Peripheral blood polymorphonuclear leucocytes (PMNs) were isolated from six normal individuals and from 27 patients with rheumatoid arthritis (RA) by the Ficoll-Hypaque rapid single step centrifugation technique, fixed in suspension, and examined by scanning electron microscopy (SEM). In addition, four of the preparations from normal individuals and eight from patients with RA were examined by transmission electron microscopy (TEM). Most PMNs in preparations from normal subjects were spherical, unpolarised, and had their surface membrane elaborated into irregular ridges and small ruffles; they contained few phagocytic vacuoles and large numbers of electron dense primary and secondary granules. A minority of the cells were non-spherical, polarised, and had portions of their surface membrane elaborated into ruffled pseudopodia. In contrast, preparations of RA PMNs frequently contained fewer unpolarised PMNs and a higher number of polarised PMNs than did preparations of normal PMNs. Some preparations of RA PMNs also contained substantial numbers of spherical cells whose surface was covered mainly by bulges and blebs. Concurrent examination by TEM showed that RA PMNs frequently contained more phagocytic vacuoles and fewer electron dense primary and secondary granules than normal PMNs. The morphological and ultrastructural changes seen in RA PMNs resembled those which normal PMNs are known to undergo on exposure to C5a in vitro, during adherence to endothelial cells in vivo, or during phagocytosis in vivo or in vitro. Our observations, therefore, provide a useful morphological correlation to those in vitro studies in which differences in the functional activity of RA and normal PMNs have been shown. The possibility that the difference seen between RA and normal PMNs is artefactual and does not represent the genuine in vivo states of these cells is discussed.
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