PROTECTION OF GERMINAL-CENTERS FROM COMPLEMENT ATTACK - DECAY-ACCELERATING FACTOR (DAF) IS A CONSTITUTIVE PROTEIN ON FOLLICULAR DENDRITIC CELLS - A STUDY IN REACTIVE AND NEOPLASTIC FOLLICLES

The development of B-cell memory is linked to the presence of germinal centres. This process is dependent on the presence of antigen, usuall y in the form of immune complexes with antibody, on the surface of the follicular dendritic cells (FDCs) that form a network in the germinal centre. The presence of immune complexes poses a constant danger of a ctivating complement. Decay accelerating factor (DAF, CD55) and the me mbrane attack complex (MAC) inhibitor (CD59) are two cell proteins who se sole function is to protect cells from the action of complement, th e former affecting the earlier components of the complement cascade, a nd the latter the terminal ones; both are bound to the cell surface vi a a glycosylphosphatidylinositol link. DAF but not CD59 could be demon strated on FDCs. DAF is also present on the FDCs in follicular lymphom as despite the absence of complement (C3) in neoplastic follicles. Thi s indicates that DAF is constitutive to FDCs but does not preclude the possibility that its expression is increased when immune complexes ar e deposited.