CTLA4-mediated trogocytosis is promoted by TCR stimulation. (A and B) Flow cytometry histograms showing total and surface levels of CD28 and CTLA4 on indicated Jurkat cells. Total and surface staining was conducted with permeabilized and unpermeabilized cells, respectively. Numbers in parentheses indicate percentages of surface CD28 or CTLA4. (C) Schematics of a Jurkat:Raji coculture assay examining CD28 or CTLA4-mediated trogocytosis (acquisition) of B7 and MHC from APCs. (D) Effects of CTLA4 or CD28 blockade on the abilities of indicated Jurkat to acquire CD80, CD86, or MHCII. Representative flow cytometry histograms and MFI values showing the CD80-GFP (reflecting total CD80), anti-CD80 (reflecting surface CD80), CD86-GFP (reflecting total CD86), anti-CD86 (reflecting surface CD86), or anti–HLA-DR (reflecting surface MHCII) in indicated Jurkat after a 15-min incubation with Raji (CD80^−/−CD86^−/−CD80-GFP⁺) or Raji (CD80^−/−CD86^−/−CD86-GFP⁺) cells under the indicated conditions. Bar graphs immediate right show the normalized MFI (norm MFI) values of acquired CD80-GFP, anti-CD80, CD86-GFP, anti-CD86, or anti–HLA-DR on Jurkat cells, calculated by setting the MFI of “CD28^−/− Jurkat −, −, −, −” condition as 0 and the condition with the highest MFI value as 100 in each replicate. Error bars are SD from three independent coculture experiments performed on three different days. *, P < 0.05; **, P < 0.01; ***, P < 0.001; unpaired two-tailed Student’s t test.