Fig. 4.

Cellular responses to PrP^REC correlate with humoral responses. (A) Thymidine incorporation into lymph node cells 48 h after in vitro restimulation with PrP^REC. Lymph node cells were taken from mice that had been immunized with PrP^REC in CFA 7 days earlier and were cultured for 48 h in the presence or absence of PrP^REC. The proliferation index represents the ratio of thymidine incorporation of antigen-stimulated to unstimulated cells. Each symbol summarizes triplicate cultures from one individual mouse (results from three independent experiments). The dotted line represents a ratio of 1 and corresponds to the thymidine incorporation of unstimulated cells. (B) CFSE stains from lymph node cells of immunized Prnp^o/o, Prnp^+/+, and MBP-PrP mice 4 days after in vitro restimulation with PrP^REC. Prnp^+/+-immunized mice showed poor or no proliferation of B220⁺ (B cells) or CD8⁺ (cytotoxic T cells) and totally unresponsive CD4⁺ (T helper cells), whereas Prnp^o/o and MBP-PrP mice showed comparable proliferation in B and CD4⁺ T cells. CD8⁺ T cells were only moderately proliferative on some of the MBP-PrP mice. Proliferation index represents the ratio of the percentage of proliferating PrP^REC-stimulated cells (lower CFSE intensity) to that of unstimulated cells. Results are of two independent experiments (Prnp^o/o and Prnp^+/+ n = 5, MBP-PrP n = 6). (C) CFSE stains from lymph node cells of immunized Prnp^o/o, Prnp^+/+, and MBP-PrP mice 4 days after in vitro restimulation with the antigen (PrP^REC or KLH). One representative mouse of each genotype is depicted.