Conversion of individual phosphatidates into rat brain lipid in vitro.

with the chloroform-insoluble residue, the lower-phase lipids and the upper-phase fraction. Only the upper-phase material showed any ability to absorb antibody, and then only when phosphatidylcholine was added as auxiliary lipid. Immunofluorescence of the cells was investigated by the indirect method by using fluorescein isothiocyanate-conjugated anti-(rabbit globulin) antiserum. By using this technique again only a fraction (1 6-27 %) of the cells were found to give a positive reaction. The appearance was typical of cell-membrane antigens, namely bright peripheral staining that did not usually involve the whole membrane. The smaller proportion of reactive cells detected by this procedure presumably reflects the threshold for detection. It also indicates further heterogeneity in the cell population with respect to this antigen, which may be useful in further characterizing these cells.