Figure 6. Ligation of OX40 during an acute P. yoelii infection bolsters the anti-parasitic and B cell helper capacity of Plasmodium-specific, Th1-like Ly6C⁺ memory CD4 T cells.

(A–F) Mice were infected with 1×10⁶ Py and administered either control rIgG or agonistic α-OX40 antibodies on days 7 and 10 p.i.

(A) MSP1₁₉-specific serum IgG2b titers in Plasmodium-infected mice seeded with either Ly6C^lo or Ly6C^hi memory CD4 T cells.

(B) On day 50 p.i., Ly6C⁺ and Ly6C^lo memory CD4 T cells were sort-purified from rIgG- and α-OX40-treated mice and co-cultured with naïve (CD19⁺IgD^hi) B cells in the presence of α-CD3ε and α-IgM. Secreted IgG was measured on day 5.

(C) Ly6C⁺ and Ly6C^lo memory CD4 T cells from rIgG- and α-OX40 treated-mice were sort-purified and transferred (2×10⁵) into Tcrα^−/− mice. Recipients were infected the following day. Parasite burdens on day 16 p.i. are shown.

(D,E) Proportion (D) and summary (E) of class-switched (IgD^loIgM^lo) germinal center B cells (GL-7⁺CD95⁺) in Tcrα^−/− mice seeded with Th1-like Ly6C⁺ memory CD4 T cells derived from either rIgG- or α-OX40-treated donors.

(F) MSP1₁₉-specific serum IgG titers in memory CD4 T cell recipient Tcrα^−/− mice on day 16 p.i.

Data (Mean +/− SD) in (A–F) are from 5 mice/group, represent 2–3 independent experiments, and were analyzed by either Student’s t tests (A,B, D–F) or one-way ANOVA (C). *p<0.05 **p<0.01. N.S. = not significant.