REGULATION OF DENDRITIC CELL NUMBERS AND MATURATION BY LIPOPOLYSACCHARIDE IN-VIVO

Dendritic cells (DC) are described as ''nature's adjuvant,'' since the y have the capacity to sensitize T cells in vivo upon first encounter with the antigen. The potent accessory properties of DC appear to deve lop sequentially. In particular, the ability to process antigens and t o sensitize naive T cells develops in sequence, a process termed ''mat uration'' that is well described in vitro. Here, we obtain evidence fo r maturation in vivo in response to the bacterial product lipopolysacc haride (LPS). Before LPS treatment, many DC are found at the margin be tween the red and white pulp. These cells lack the M342 and DEC-205 ma rkers, but process soluble proteins effectively. 6 h after LPS, DC wit h the M342 and DEC-205 markers are found in increased numbers in the T cell areas. These cells have a reduced capacity to process proteins, but show increases in the B7 costimulator and T cell stimulatory capac ity, 48 h after LPS, the number of DC in the spleen is reduced markedl y. We interpret these findings to mean that LPS can cause DC in the ma rginal zone to mature and to migrate into and then out of the T cell a reas.