THE RELATIONSHIP OF BLOOD-LYMPHOCYTES TO THE RECIRCULATING LYMPHOCYTEPOOL

Lymphocyte recirculation facilitates the detection and elimination of pathogens and the dissemination of immunologic memory. It is generally assumed that all small lymphocytes in the blood are actively recircul ating, yet there is little quantitative data directly comparing the mi gration of this population with actively recirculating, lymph-derived lymphocytes. In this study blood lymphocytes were labeled with fluores cein isothiocyanate (FITC), and lymph lymphocytes were labeled with CM -Dil, reinfused intravenously, and monitored in blood and lymph, After equilibration the concentration of blood lymphocytes was several time s higher in blood than in lymph, whereas lymph lymphocytes displayed t he opposite behavior. This suggested that blood lymphocytes did not re circulate as efficiently as lymph lymphocytes, so we examined the foll owing blood lymphocyte subsets in greater detail: B cells, CD4(+), CD8 (+), and gamma delta T cells. Within 4 hours postinjection the percent age of FITC+ CD8(+) and CD4(+) lymphocytes fell in the blood and remai ned significantly lower than the injected sample, In contrast, the con centration of FITC+ gamma delta T cells did not change, and the percen tage of FITC+ B cells increased. These data suggest that subpopulation s of B and perhaps gamma delta T lymphocytes in the blood do not recir culate efficiently through lymph nodes. (C) 1998 by The American Socie ty of Hematology.