The effect of methotrexate on in vitro immunoglobulin production.

The effect of Methotrexate (MTX) on pokeweed mitogen (PWM) induced immunoglobulin (Ig) production in vitro was studied over a range of 10(-4) - 10(-12)M MTX, using an enzyme-linked-immunosorbent assay (ELISA). MTX, at a concentration of 5 X 10(-9)M profoundly decreased all classes of Ig production, IgM greater than IgG greater than IgA. Plasma cell numbers, identified using polyclonal antihuman immunoglobulin, demonstrated a similar sensitivity to MTX. There was a paradoxical increase in IgM and IgG production at 5 X 10(-11)M MTX. Clinical implications of these findings are discussed.