T-LYMPHOCYTES FROM NORMAL HUMAN PERITONEUM ARE PHENOTYPICALLY DIFFERENT FROM THEIR COUNTERPARTS IN PERIPHERAL-BLOOD AND CD3(-) LYMPHOCYTE SUBSETS CONTAIN MESSENGER-RNA FOR THE RECOMBINATION ACTIVATING GENE RAG-1

The surface antigens of peritoneal lymphocytes of healthy human individuals were studied, B lineage cells comprised 2.3% of the total peritoneal lymphocyte population. Although the majority of peritoneal cavity lymphocyte (PCL)T cells expressed alpha beta T cell receptor (TcR), up to 17% expressed gamma delta TcR. The majority of PCL exhibited markers of the thymus-dependent lineage (CD2(+) CD3(+) TcR alpha beta(+) CD4(+) or CD8 alpha(+)beta(+)) and surface antigens associated with memory and activation (CD45RO(+) CD11a(+) CD18(+) CD49d(+) HLA-DR). Up to 92% of both CD4(+) and CD8(+) T cells bore CDw60, thus characterizing the T cell subset containing helper activity for mitogen-driven B cell differentiation. The majority of PCL T cells were CD8(+) and, in addition, up to 60% of this population expressed the homodimeric CD8 alpha(+)beta(-). Messenger RNA for the recombination activating gene RAG-1 was examined in CD3(-) PCL depleted of CD19(+) lineage cells. The PCL population which comprised cells containing RAG-I mRNA transcripts was CD19(-), surface IgM(-): cytoplasmic IgM(-) and CD2(-) CD3(-) CD4(-) CD8(-) CD56(-). However, this population was CD7(+) (approx. 75%), and contained both CD7(-)CD34(+) (up to 3%) and CD7(+) CD34(+) (up to 3%) cells. These findings are compatible with the hypothesis that the adult human peritoneum provides a microenvironment capable of supporting a thymus-indenpendent differentiation of T lymphocytes.