Immunohistochemical and flow cytometric detection of T cells and granulocytes in inflamed ankle joints of severe combined immunodeficient (SCID) mice with adoptively transferred proteoglycan-induced arthritis (PGIA). The SCID mouse used for immunohistochemistry developed arthritis 9 days after receiving unlabeled cell transfer and was re-transferred with CellTracker Red-labeled T cells and unlabeled non-T cells on day 10. In vivo two-photon microscopy imaging of the inflamed ankle on day 12 revealed no red fluorescent cells. The mouse was sacrificed, and frozen sections were prepared from the ankle after imaging. (a) No red fluorescent T cells are visible in the unstained section of the inflamed ankle. (b) Immunostaining with green fluorophore-conjugated anti-CD4 monoclonal antibody (mAb) shows no evidence of CD4+ T helper cells (no yellow or green color). (c) Anti-Gr-1 mAb against granulocytes stains numerous cells in the same joint. Scale bars, 100 μm. St, synovial tissue. (d) Flow cytometry of synovial fluid cells from the arthritic ankle joints of a SCID mouse shows a small population of T cells, nearly all of which are CD4+, in the fluid. (e) Synovial fluid from arthritic SCID ankles contains a large proportion of Gr-1hi granulocytes that also express high levels of CD11b. Flow cytometry was done using synovial fluid samples from SCID mice that developed PGIA approximately 2 weeks after transfer of unlabeled cells from arthritic donors. Flow data are representative of at least six synovial fluid samples harvested from inflamed ankle joints of SCID mice with adoptively transferred PGIA.