Enhancement of Human B Lymphocyte Differentiation in Vitro by Thyroid Hormone.

A study was made of the regulatory influence of a thyroid hormone, triiodothyronine (T_a), on human blood T- and B-lymphocyte responses in vitro. Blood lymphocytes were stimulated with the T-cell mitogens concanavalin A (Con A) and phytohaemagglutinin (PHA), with the T-dependent B-cell activator pokeweed mitogen (PWM), and with the T-independent B-cell activator Staphylococcus aureus Cowan I bacteria in the presence of various hormone concentrations. T₃ did not stimulate T-cell proliferation. The number of immunoglobulin-containing and -secreting cells (plasmablasts) was increased in PWM and Staph. aureus cultures treated with T₃. The maximal enhancement was reached at a concentration of 10^-9-10^-7 M T₃. Cell fractionation techniques revealed that T₃ apparently had a direct stimulatory effect on B-cell differentiation. [ABSTRACT FROM AUTHOR]