Surface markers of small lymphocytes appearing in the mouse Ehrlich ascites tumour, host spleen and blood.

Small lymphocytes sampled from intraperitoneally growing Ehrlich ascites tumour in CBA/H-T mice as well as host spleen and blood at different days of tumour development were characterized radioautographically on the basis of two surface markers, IgM for B cells and θ antigen for T cells. A direct binding of I-labelled anti-IgM detected natural surface IgM, while an indirect binding following a prior exposure to anti-θ antibody detected θ antigen. Cells remaining unlabelled with the latter procedure were considered to lack both markers (double negative). While the incidence of IgM+ve small lymphocytes within the tumour declined, their absolute numbers increased with tumour growth. Low levels of antiglobulin binding shown by these cells were considered to reflect low levels of maturation, because (1) our previous studies indicated that they were newly formed, and (2) the extent of antiglobulin binding by B lymphocytes in the marrow is known to increase with increasing post-mitotic age. The proportions and the absolute numbers of θ+ve as well as the double negative small lymphocytes increased within the growing tumours. Within the host spleen, the incidence of IgM+ve small lymphocytes remained unchanged but their absolute numbers increased because of splenomegaly. The degree of antiglobulin binding by these cells was comparable to that of the normal splenic population. The incidence of θ+ve cells dropped but their absolute numbers remained unchanged in the spleen during tumour growth. In contrast, the incidence as well as the absolute numbers of double negative cells increased markedly. This cell category increased also in the blood, possibly in transit to the tumour site and other lymphoid organs from the bone marrow, where they were most prevalent. Their bone marrow origin was further suggested by a preponderance of marrow derived small lymphocytes at the tumour site as well as in the host spleens found in our earlier studies. Double negative population in the spleen showed a paucity of C′3 and Fc receptors on the cell surface and included cells capable of producing B lymphoid colonies .