OX40 promotes T cell accumulation in a dose dependent manner.

(A, B) Equal numbers of WT (CD45.1+CD45.2−) and OX40−/− (CD45.1+CD45.2+) smtg were transferred into the same WT recipients (CD45.1−CD45.2+) prior to LCMV cl13 infection. Splenocytes were harvested on days 5, 8, 10 and 20 post infection (n = 4–8 for each time point) and (A) frequencies of OX40−/− smtg and WT smtg were determined within the CD4 gate by flow cytometry. (B) Frequencies shown in FACS-plots are percent of CD45.1+ (transferred cells); plots are gated on CD4 T cells. (C–E) OX40+/+ (WT, black bars), OX40+/− (Het, grey bars) and OX40−/− (KO, white bars) smtg were separately transferred into WT recipients prior to LCMV cl13 infection and (C) frequencies of WT, Het and KO smtg cells within the CD4 gate were determined 10 days post infection (n = 5 per group). (D) OX40 expression on WT, Het and KO smtg cells was determined 10 days post infection by flow cytometry (n = 5 per group). (E) Representative FACS-plots showing transferred cells and OX40 expression gated on CD4 T cells. (F) Equal numbers of CD45.1/2 mismatched WT and OX40−/− P14 cells were co-transferred into WT recipients prior to LCMV cl13 infection and frequencies of OX40−/− P14 and WT P14 were determined within the transferred P14 population by flow cytometry on day 3, 5, 8 and 20 post infection (n = 4–5 for each time point). (G, H) Similar co-transfer experiments with CD4 and CD8 T cell were performed in order to compare the role of OX40 on a single cell level in acute and chronic LCMV infection. Graph shows percentage of transferred OX40−/− CD4 respectively OX40−/− CD8 T cells of all transferred T-Cells 8 days post infection. Data are derived from 2–3 independent CD4 smtg cell transfer experiments per time point and 1–3 independent CD8 P14 cell transfer experiments per time point.