The human lymph node germinal center cell: characterization and isolation by using two-color flow cytometry.

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Abstract
The germinal center of lymphoid tissues is a critical microenvironmental site of B cell activation and differentiation in response to antigenic stimuli. However, characterization of germinal center cells (GCC) in tissue sections has proved technically difficult. Therefore, we have employed two-color flow cytometric analysis of suspended human tonsillar lymphocytes in order to define more precisely the immunologic features of GCC. These cells were identified in suspension by virtue of their specific surface binding of the lectin peanut agglutinin (PNA), confirmed by tissue immunoperoxidase studies. Phycoerythrin-labeled lectin was used in combination with a variety of fluorescein-labeled antibodies in order to identify subpopulations of tonsillar lymphocytes. The majority of PNA+ cells were B cells, and both PNA+ and PNA- B cells stained for surface immunoglobulin light chains. PNA+ cells lacked surface IgD, but included cells with surface IgG and IgM. Both PNA+ and PNA- cells stained for B1, B2, BA-1, Leu-12, Leu-14, CR-I, and HLA-DR antigens, whereas CALLA was present only on PNA+ cells. There were differences between PNA+ and PNA- cells in the relative expression of B1 and B2 antigens, possibly reflecting differences in B cell activation or maturation. A small proportion of T cells were PNA+, including both helper/inducer and suppressor/cytotoxic phenotypes. PNA+ cells included both small and large lymphoid cells, and almost all DNA synthetic activity was associated with the large PNA+ cells. PNA+ B cells isolated by cell sorting had morphologic features characteristic of GCC. Therefore, PNA+ cells in suspension appeared to represent GCC, and features of these cells that cannot be convincingly shown in tissue section studies were demonstrated by flow cytometry.