C-reactive protein is one of the major plasma proteins that increases dramatically in concentration during the acute phase response. The protein is produced mainly in the liver, and in serum it may be elevated 2000 fold by inflammatory events and other pathological processes (Abernathy & Avery, J. Exp. Med., 73 , 173-182, 1941). There is evidence that the biosynthesis of CRP is under the control of distinct cytokines (Ganter et al, EMBO J. , 8, 3773-3779, 1989).

The protein is so called because of its ability to bind to and be precipitated by the C-polysaccharide of Streptococcus pneumoniae. The molecular weight of the subunit is around 21,000 and each subunit associates in a discoid arrangement composed of five such units (Gotschlich & Edelman, Proc. Natl. Acad. Sci., 54, 558-565, 1965).

The measurement of CRP in serum is important for diagnosing pneumococcal infections and other infectious diseases. The titer of the serum is maximal in the active stage of the disease, and decreases rapidly after the onset of convalescence.