Increased soluble CD4 molecules and the role of soluble CD4 production in patients with rheumatoid arthritis.

We investigated the concentration of soluble CD4 molecules (sCD4) in serum, and the mechanism of sCD4 production from T lymphocytes, in patients with rheumatoid arthritis (RA). The concentration of sCD4 molecules was determined using a solid-phase enzyme-linked immunosorbent assay method. Using reverse transcription polymerase chain reaction (RT-PCR) techniques, we studied the presence of alternatively spliced mRNA encoding the transmembrane site of CD4, and the mRNA encoding a conservative region of the CD4 binding site of the human immunodeficiency virus (HIV), in the serum of RA patients. Levels of sCD4 found in RA patients were higher than in normal controls (199 U/ml compared with 8.4 U/ml, respectively), and correlated with additional medical parameters. The results of RT-PCR suggested that the higher sCD4 levels may be due to shedding from the cell membrane after protease digestion, not to alternative splicing or a reaction to viral binding to sCD4.