Abstract
The immunoglobulins are built from two identical heavy and two identical light chains. However, more light than heavy chains are produced under physiological conditions.
Thus, the free light chains (FLC) may be detected in serum and other biological fluids using sensitive and specific quantitative nephelometric assay. Changes of FLC level in serum are associated with monoclonal proliferation or polyclonal activation of B cells, and with deficiency of renal functions.
Monoclonal proliferation of B cells is associated with high serum level of FLC kappa or lambda, and abnormal relation of FLC kappa : FLC lambda. Polyclonal activation of B cells is associated with high serum level of both FLC, and normal relation of FLC kappa : FLC lambda.
Both types of these changes are important in rheumatic diseases. Serum changes of monoclonal FLC are present in the following main conditions: (1) In differential diagnosis of non-inflammatory back pain persisting more than one month, because this type of back pain may be present as early manifestation of multiple myeloma or any other monoclonal gammopathy, and (2) also in depistage of B cell lymphoma in primary Sjögren's syndrome or another diffuse connective tissue disease.
High serum level of both FLC is useful biomarker of activity in systemic lupus erythematosus (SLE) incl. follow- up controls of flare. The monitoring of FLC serum level in SLE and rheumatoid arthritis is also successfully used as sensitive biomarker of response to anti CD20 therapy by means of rituximab.