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REVIEW: Unknown Functions of Immunoglobulins A


T. N. Kazeeva and A. B. Shevelev*

Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, 119071 Moscow, Russia; fax: (495) 954-2732; E-mail: shevelev@inbi.ras.ru

* To whom correspondence should be addressed.

Received October 25, 2006; Revision received February 4, 2007
Traditionally, the function of immunoglobulins A (IgA), the major type of secreted antibodies, has been thought to be restricted to binding antigens outside the epithelium basal membrane. Therefore, effector mechanisms eliminating IgA-opsonized targets have not been investigated so far. However, some indirect observations of infectious agents penetrating into tissues and blood from the environment suggest such mechanisms (analogous to IgG/IgM-dependent activation of complement and natural killers). In the present review, we examine details of IgA structure that might contribute to elucidation of IgA-dependent effector functions in human and animal immunity. Special attention is given to a putative transduction of signal about antigen binding in the active center of IgA from the Fab- to the Fc-superdomain via intramolecular conformational rearrangements. Different structure of the IgA subclasses (IgA1 and IgA2) is examined taking into account probable divergence of their functions in immune response.
KEY WORDS: secretory immunity, IgA, antibodies, effectors, IgA1-proteases, CD89, respiratory burst

DOI: 10.1134/S0006297907050045