Increased production of interleukin-6 by T lymphocytes from patients with multiple myeloma.

Alterations in T lymphocyte functions may affect other cellular components of the immune system. Several lymphokines produced by T cells are involved in the proliferation and differentiation of human B lymphocytes. Alterations in the secretion of these molecules may be implicated in the development of B cell lymphoproliferative diseases. We have investigated the production of interleukin-2 (IL-2) and interleukin-6 (IL-6) by T lymphocytes from 14 patients with multiple myeloma (MM) and 16 healthy controls. The phenotypical and functional characteristics of these T lymphocytes were also studied. The proliferative response to vegetal lectin phytohemagglutinin (PHA) stimulation was decreased in T lymphocytes from MM patients (p < 0.01). This defective proliferative response cannot be ascribed to either defective IL-2 production or diminished receptor expression, since neither of these parameters showed a significant difference between MM patients and healthy controls (p < 0.05). However, the defective proliferative response of T lymphocytes from MM patients was reverted by the addition of saturating amounts of exogenous IL-2 (p > 0.05) but not by exogenous IL-6 (p < 0.05). The IL-6 production by PHA-stimulated T lymphocytes from the MM patients was significantly higher than in healthy controls (p < 0.01). We conclude that T lymphocytes from MM patients show a functional alteration with a defective proliferative response to PHA that is reverted by exogenous addition of IL-2. After lectin stimulation, the production of IL-2 by T lymphocytes from those patients was normal, while IL-6 secretion was increased.