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Protein A from Staphylococcus aureus is known to interact in a specific manner with most subclasses of mammalian IgG, In our present work we have used protein A labeled with fluorescent or radioactive markers as a probe to detect cell‐associated IgG molecules. Using this approach to study human lymphocytes or lymphoid cell lines, we have found it possible to assess with accuracy the percentage of cells in a given population that carry a certain surface marker. Precise measurements can also be made as to quantities of cell surface‐attached IgG molecules, thereby allowing determinations of antigenic site numbers per cell in a new and simplified manner. We report here in detail the actual technical procedures involved, together with tests for human cell surface structures, including immunoglobulin molecules of IgG and other classes, HL‐A antigenic sites, beta2‐microglobulin, and T lymphocyte‐specific antigens

In order to further understand Epstein-Barr virus (EBV)-lymphocyte interactions, we investigated a chain of events including: (i) EBV binding to human lymphocyte subpopulations; (ii) the earliest appearance of EBV-determined nuclear antigen (EBNA) in the lymphocytes after EBV infection; and (iii) establishment of continuous lymphoblastoid cell lines (LCL) by infecting with EBV different types of lymphocyte preparations from the same as well as from different donors. By using direct membrane immunofluorescence assay, we found that only a small fraction of human peripheral blood and cord blood lymphocytes (CBL), and possibly less than 31% of the T cell-depleted lymphocyte population, carry receptors for P3HR-1 strain of EBV. The number of cells carrying receptors for EBV did not vary considerably among different blood lymphocyte populations from several normal donors. EBV adsorption on lymphocyte subpopulations showed that purified thymus-dependent (T) cells and thymocytes did not adsorb EBV, in contrast to T cell-depleted lymphocyte populations and lymphoid cells from fetal liver and spleen. In CBL infected with EBV strain B95-8, EBNA was detected by anti-complement immunofluorescence as early as 18 h after infection. This indicates that EBNA is the earliest detectable EBV-determined intracellular antigen to appear after infection and before or during lymphocyte transformation by EBV. Transformation was observed only in lymphocyte cultures containing detectable thymusindependent B cells but not in cultures of purified T cells. With one exception (ES-B-1), all the EBV-transformed LCL from different origins carried surfacebound immunoglobulins (a B cell marker). These included also the 10 LCL obtained by infecting cultures of adherent cells from different donors. With regard to its surface markers, ES-B-1 appeared to be an exceptional EBV genome-carrying line, and it also lacked the ability to form spontaneous rosettes with sheep erythrocytes (a T cell marker). Therefore, it is possible that ES-B-1 was derived from an atypical B cell or B cell precursor or from a so-called "null cell" transformed by EBV.Transformation of human and simian lymphocytes into established lymphoblastoid cell lines (LCL) is a well-known biological property of Epstein-Barr virus (EBV) (4,6,14,19).Transformation of thymus lymphoid cells by EBV and the establishment of several LCL from these cultures was reported by Pope et al. (19) in 1968. However, when cells of seven of these lines (kindly supplied by J. H. Pope) were examined in our laboratory, it was found that they did not form spontaneous rosettes with sheep erythrocytes (SRBC) and that they had Present address: Institute of Pathology, School of Veterinary Medicine, Hannover, West Germany.readily detectable amounts of surface-bound immunoglobulins (unpublished data); these two features are characteristic of human thymusindependent B lymphocytes (3,9). Recently, Pattengale et al. (17) reported that transformation could not be obtained by infecting fetal thymocytes with EBV. Jondal and...