Homotypic cluster formation of dendritic cells, a close correlate of their state of maturation. Defects in the biobreeding diabetes-prone rat.

Aggregation of dendritic cells (DCs) in homotypic clusters has been described in vivo in lymph and skin, and here we report studies on homotypic clustering of rat splenic (s) DCs in vitro. Wistar rat sDCs readily formed homotypic clusters in culture, which increased in number and size over time (with a peak at t = 3 h). Keeping the cells at higher densities or treatment with anti-CD43 induced more and larger homotypic clusters. After such enhanced clustering the DCs had increased their T cell stimulating capabilities in syngeneic mixed lymphocyte reaction, and had a higher expression of CD80 and CD86 (signs of maturation). Ag transfer from bovine serum albumin-fluorescein isothiocyanate-pulsed to unpulsed DCs was observed during clustering. Here we also show that sDCs of the biobreeding diabetes-prone (BB-DP) rat, a model of autoimmune diabetes/thyroiditis, formed fewer and smaller clusters than Wistar sDCs, and that DC-DC clustering resulted in only a modest maturation of the cells (as determined in syn MLR and by phenotyping). Anti-CD43 completely restored the clustering defect BB-DP DCs in vitro, yet T cell-stimulating capability was only restored to a limited extent. Ag transfer in BB-DP DC clusters was similar.