Rejection of HY-disparate skin grafts via peripherally expanded lymph node cells is critically dependent on the size of the starting inocula.
(A) Adult thymectomized, C57BL/6 females were T cell depleted and grafted with male tail skin as described in “Materials and methods.” Primed cells were collected from the draining LN of T-cell–replete syngeneic female mice 3 weeks after successful male skin graft rejection, teased into a single-cell suspension, and injected via the tail vein 24 hours after skin grafting. Unprimed cells were collected from LN of T-cell–replete females naive to male antigen. Percent surviving grafts are shown as measured by visual inspection as described in “Materials and methods.” Thymectomized, T-cell–depleted mice (TXY/TCD mice) receiving 5 × 106primed LN cells are partially able to reject HY-disparate skin grafts (▪, n = 4) when compared to mice receiving no LN inocula (●, n = 5). When the LN cell dose is increased to 10 × 106, there is rejection in all mice but the rate of graft rejection remains delayed (♦, n = 5). At a dose of 25 × 106 LN cells (▴, solid line, n = 5), graft rejection occurs at a rate analogous to thymus-bearing control animals (▾, dashed line, n = 6) also receiving primed inocula. Note the modest effect of the primed inocula when this group is compared to thymus-bearing animals receiving an unprimed inocula (▿, dashed line, n = 5). (B) To assess primary immune responses, TXY/TCD mice were given graded numbers of LN cells from syngeneic females naive to male antigen via tail vein. The mice were then sensitized by intraperitoneal injection of 1 × 105 enriched male dendritic cells from male splenocytes as described in “Materials and methods.” These cells express B7-1, B7-2, CD11c, and major histocompatibility complex (MHC) class II and represent 50% to 60% of the cells injected in all experiments. Twenty-one days after LN cell transfer and enriched male dendritic cell sensitization, the mice were grafted with male tail skin as before and observed for rejection. As with the recall responses, mice receiving 1 × 106 naive cells were unable to reject HY-disparate skin grafts (●, n = 5). Administration of 10 × 106 naive cells led to graft rejection in all of the mice but at a delayed rate (▪, n = 7). Transfer of 25 × 106 LN cells (⧫, n = 7) completely restored responses so that rejection occurred at similar rate to thymus-bearing control groups receiving enriched dendritic cells (▴, dashed line, n = 6). Thymus-bearing control groups receiving no enriched dendritic cells (▾, dashed line, n = 5) required approximately 2 weeks longer to reject HY grafts.
