Francesca Granucci

The signals controlling the checkpoints of dendritic cells (DC) maturation and the correlation between phenotypical and functional maturational stages were investigated in a defined model system of growth factor-dependent immature mouse DC. Three sequential stages of DC maturation (immature, mature, and apoptotic) were defined and characterized. Immature DC (stage 1) had low expression of costimulatory molecules, highly organized cytoskeleton, focal adhesion plaques, and slow motility; accordingly, they were very efficient in antigen uptake and processing of soluble proteins. Further, at this stage most of major histocompatibility complex class II molecules were within cytoplasmic compartments consistent with a poor allostimulatory capacity. Bacteria or cytokines were very efficient in inducing progression from stage 1 towards stage 2 (mature). Morphological changes were observed by confocal analysis including depolymerization of F-actin and loss of vinculin containing adhesive structures which correlates with acquisition of high motility. Antigen uptake and presentation of native protein antigen was reduced. In contrast, presentation of immunogenic peptides and allostimulatory activity became very efficient and secretion of IL-12 p75 was detectable after antigen presentation. This functional DC maturation ended by apoptotic cell death, and no reversion to the immature phenotype was observed.

Viral infection is sometimes associated with the initiation or exacerbation of autoimmune disease, although the underlying mechanisms remain unclear. One proposed mechanism is that viral determinants that mimic host antigens trigger self-reactive T cell clones to destroy host tissue. An epitope expressed by a coat protein of herpes simplex virus-type 1 (HSV-1) KOS strain has now been shown to be recognized by autoreactive T cells that target corneal antigens in a murine model of autoimmune herpes stromal keratitis. Mutant HSV-1 viruses that lacked this epitope did not induce autoimmune disease. Thus, expression of molecular mimics can influence the development of autoimmune disease after viral infection.