Co-expression of the CD45RA and CD45RO antigens on T lymphocytes in chronic arthritis.
The site of T lymphocyte activation in chronic arthritis is unknown. Peripheral blood (PB) lymphocytes from chronic arthritis patients are in a 'naive' or non-activated state, as defined by expression of the CD45RA antigen and lack of HLA class II expression. In contrast, most synovial fluid (SF) T lymphocytes express a 'memory' or activated phenotype, as defined by the CD45RO antigen and high HLA class II expression. Following stimulation, naive cells lose CD45RA and gain CD45RO expression to become memory cells with a transitional stage of dual CD45RA, CD45RO antigen expression. To localize where this change in phenotype occurs we used dual colour immunofluorescence labelling to compare the percentage of dual CD45RA, CD45RO-positive T lymphocytes in PB and SF from chronic arthritic patients and from normal PB, assuming this population would be increased at the primary site of T lymphocyte activation. Expression of the intermediate and late activation marker, HLA-DR, was also analysed using dual colour immunofluorescence labelling. The percentage of dual positive T lymphocytes was similar between arthritic PB, SF, and normal PB, as was the density of both CD45RA and CD45RO antigens. Thus, CD45 isoform expression did not indicate where T lymphocytes were activated. However, we identified a previously unreported population of CD45RA+ CD45RO+ HLA-DR- T lymphocytes in arthritic and normal PB. In SF, this population was absent, but a substantial number of dual CD45RA, CD45RO-positive HLA-DR+ T lymphocytes were identified. This population would not be predicted by the current model of T lymphocyte activation. Division of T lymphocytes into functional groups on the basis of CD45 isoform expression is likely to be more complicated than previously thought. Based on our findings we propose an alternative model of T lymphocyte differentiation.
Summers
K L
KL
Haematology/Immunology Research Group, Christchurch Hospital, New Zealand.
O'Donnell
J L
JL
Hart
D N
DN
D001168:Arthritis / Q000097:blood / Q000276:immunology* / Q000473:pathology; D002454:Cell Differentiation; D002908:Chronic Disease; D005455:Fluorescent Antibody Technique; D006684:HLA-DR Antigens / Q000378:metabolism; D006801:Humans; D007156:Immunologic Memory; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D008213:Lymphocyte Activation; D008954:Models, Biological; D010641:Phenotype; D013582:Synovial Fluid / Q000166:cytology / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000473:pathology
D006684:HLA-DR Antigens; D017493:Leukocyte Common Antigens