UMBILICAL-CORD BLOOD LACKS CIRCULATING B-LYMPHOCYTES EXPRESSING SURFACE IGG OR IGA

In vitro umbilical cord blood B lymphocytes fail to form IgG and IgA s ecreting plasma cells when stimulated with Pokeweed mitogen, Since pre vious investigators have found percentages of B lymphocytes expressing surface IgG or surface IgA comparable to those seen in adults, this i mplies a defect in umbilical cord blood B-lymphocyte function, We have examined surface Ig expression on umbilical cord blood B lymphocytes by flow cytometry under conditions in which serum derived Ig are rigor ously excluded, Under these conditions no B lymphocytes expressing sur face IgG or IgA, which should serve as precursors for IgG and IgA secr eting plasma cells, were observed, This finding was confirmed by compa ring the ratio of mRNA levels for immunoglobulin gamma-chain to mu-cha in in mononuclear cells by quantitative mRNA-based PCR, The ratio in u mbilical cord mononuclear dells was 10-fold less than that seen in adu lt cells, The inability of newborn peripheral blood to form IgG and Ig A plasma cells may result from an absence of appropriate precursor cel ls and not a defect in B lymphocyte maturation. (C) 1997 Academic Pres s.