DEFICIENCY IN T-CELL RESPONSES OF HUMAN FETAL LYMPH-NODE CELLS - A LACK OF ACCESSORY CELLS

Lymph node and spleen cells of human foetuses from the 18th to the 24t h week of gestation were analysed with regard to their phenotypes and their functional capacities. Fetal mesenteric lymph nodes contain high percentages of CD45RA(+) T cells and few B cells and monocytes, where as the fetal spleen is comprised of equal numbers of T and B cells as well as monocytes/macrophages. Functional analysis of lymph node T cel ls revealed a lack of proliferative response to PHA or CD3 specific mA b, despite induction of expression of the activation marker CD69. Prol ifer ation of LN cells and thymocytes was observed upon addition of ex ogenous IL-2. An allogeneic EBV transformed tumour cell line, known to be an effective antigen presenting cell, could induce proliferation o f LN cells without exogenous IL-2 and fetal spleen cells could prolife rate in response to all stimuli tested without additional IL-2. Spleni c non-T cells could restore the proliferation of lymph node cells as e fficiently as IL-2 or the EBV transformed B cell line. Separated B cel ls were more effective than plastic adherent cells on a per cell basis . Naivity of the fetal immune system is therefore not only reflected b y the expression of markers representative for naive lymphocytes but c an also be due to the absence of potential accessory cells in the diff erent lymphoid organs.