C-reactive protein antigenicity on the surface of human peripheral blood lymphocytes. Characterization of lymphocytes reactive with anti-neo-CRP

Previously, we have shown that antibodies specific for C-reactive protein determinants, not present on the native molecule, termed neo-CRP, also react with a significant percentage of PBL. In the present study, cells were evaluated by flow cytometry using α-neo-CRP antisera and mAb specific for lymphocyte subsets. With use of either monocyte-depleted PBL or Percoll-enriched large granular lymphocytes, we observed an overlap between cells reactive with α-neo-CRP and cells bearing the surface markers CD16, CD11b, Leu-7, and/or Leu-19, which are expressed on NK cells. In addition, we showed co-expression of the neo-CRP antigen with CD19, CD20, and HLA-DR, cell surface markers which are expressed on B lymphocytes. The major proportion of CD3⁺ cells failed to exhibit co-expression of neo-CRP. Single parameter flow cytometric analyses demonstrated that cells reactive with α-neo-CRP exhibited a bimodal staining pattern based on fluorescence intensity: high intensity neo-CRP(bright) and low intensity neo-CRP(dim). Two-color analysis revealed that neo-CRP(bright) cells co-expressed CD19, CD20, and HLA-DR, whereas neo-CRP(dim) cells co-expressed CD16, CD11b, Leu-7, and Leu-19. Anti-neo-CRP also reacted with PBL obtained from patients with CD16⁺ lymphoproliferative disorders and from patients with chronic lymphocytic leukemia of B cell origin, but not with cells from patients with T cell or myeloid leukemias. The α-neo-CRP cells from patients with NK cell expansions showed dim fluorescence, whereas patients with B cell expansions showed bright fluorescence, consistent with the staining patterns observed with normal PBL. In addition, cell lines of T cell, B cell, NK cell, myeloid, and erythroid origin were evaluated for reactivity with α-neo-CRP. The cloned NK cell line NK 3.3 reacted as neo-CRP(dim), but the B cell lines BL41, BL41/95, T1, T2, and CESS all reacted as neo-CRP(bright). The cell lines K562, Molt-4, Hut-78, HL-60, U-937, and THP-1-0, which lack characteristic NK and B cell markers, did not react with α-neo-CRP. Additional study of the two-color histograms revealed a distinct diagonal staining pattern that was observed only when cells were co-stained with α-neo-CRP and either α-CD16 (α-FcγRIII) or antibody IV3 (α-CDw32; α-FcγRII). This finding suggests a 1:1 relationship between FcγR on both NK and B cells and determinants recognized by α-neo-CRP. These results demonstrate that a neo-antigenic form of CRP, or a cross-reactive molecule, is present on the surface of NK and B cells, and suggests that the molecule may be physically associated with FcγR present on these cells.