Quantification of Soluble E‐Receptor in the Serum of Patients with Various Diseases and Its Accompanying in Vitro Immunosuppression in Neoplasia

Evidence in the literature indicates that soluble E‐receptor in the serum may modulate T‐dependent immune response. We have developed a solid‐phase radioimmunoassay to measure the soluble form of E‐receptor from various sources. The assay detects solubilized antigens derived from E‐receptor‐bearing T lymphocytes and not with non‐E‐receptor‐bearing B lymphocytes. The sensitivity limit of the assay is 0.1 ng/ml of purified E‐receptor antigen. Using this assay, one can show that the T‐cell mitogen phytohaemagglutinin stimulated both lymphocytes and cells of the resting human T‐cell lymphoma cell line Jurkat to shed or secrete E‐receptor into the culture medium. Results of the radioimmunoassay performed on human sera indicated that some patients with Hodgkin's disease, melanoma, sarcoma, or acute or chronic lymphocytic leukaemia had elevated levels of this antigen in their serum, whereas normal human sera registered lower levels, Elevated levels of the soluble form of E‐receptor in the serum were suggestive of an in vitro assessment of their immunosuppressive activity. These results indicate that activation of T‐cell immunity in vivo may result in humoral immunosuppression.