Evidence for membrane differentiation in polarised leucocytes: the distribution of surface antigens analysed with Ig-gold labelling

The distribution of a number of leucocyte surface antigens was studied on both round and polarised neutrophil or mononuclear leucocytes using Ig-gold conjugates with transmission electron mi-croscopy. Thin sections of cells, 'which had been lightly fixed before antibody labelling, were ana-lysed using a statistical method to determine: (1) whether the antigens had a non-random distri-bution or 'clustering ' over the cell surface; and (2) whether there was any overall bias in labelling to give a polarised distribution. Comparison be-tween the results of this analysis and cell mor-phology were made. The results indicated that with the antigens investigated here, CD45, CD15, HLA-DR and CR3, the majority of polarised cells had a calculated direction of overall asymmetry of gold particles that was aligned with the long axis of morphological polarity. Maximal asymmetry was seen in polarised cells labelled for CD45 and HLA-DR, with labelling ratios of up to 6:1 between the front and back of the cell. A number of round mononuclear cells demonstrated significant polari-sation of gold particles but this had no apparent morphological correlation and, in general, round cells showed a low degree of asymmetry. However, there was evidence that both round and polarised cells had a non-random distribution or 'clustering' of gold particles, which was more marked in mor-phologically polarised cells and particularly sig-nificant in polarised neutrophil leucocytes labelled for CR3. The significance of these results for models of cell locomotion involving membrane flow is discussed. Key words: receptor distribution, cell polarity, cell locomotion