Production of IgM rheumatoid factor by normal lymphocytes after stimulation with preparations containing IgM rheumatoid factor from patients with juvenile arthritis.

Preparations containing IgM rheumatoid factor (RF) and hidden IgM RF were isolated from the serum samples of nine patients with juvenile rheumatoid arthritis. Six of these preparations stimulated lymphocytes from normal donors to produce IgG and IgM, of which up to 11% had IgM RF activity. In contrast, the polyclonal activator pokeweed mitogen also stimulated IgM production, but only 1% had IgM RF activity. A relation between the activator and IgM RF or hidden IgM RF is suggested. This is based on the positive correlation between IgM RF concentration in these preparations and their ability to stimulate lymphocytes to produce IgG, IgM, and IgM RF. These data indicate that preparations from patients with juvenile rheumatoid arthritis containing IgM RF and hidden IgM RF are potent stimulants of lymphocytes from normal donors, with specific production of IgM RF.