Immunoglobulin free light chains and mast cells: pivotal role in T-cell-mediated immune reactions?

Immunoglobulin (Ig) free light (L)-chains have long been considered as the meaningless remnants of a spillover in the regular Ig production by B cells. The recently discovered role for Ig free L-chains in mediating hypersensitivity-like responses sheds new light on their potential role in immune responses. Ig free L-chains can sensitize mast cells, such that a second encounter with the appropriate antigen results in mast-cell activation. The possible importance of this reaction for the induction of T-cell-mediated immune reactions, leading to contact sensitivity, multiple sclerosis and rheumatoid arthritis is discussed.