Binding of heterologous anti-brain antibodies to mouse B cells.

Antibodies produced in rabbits against mouse brain are able to react with the majority of lymph node and spleen murine lymphocytes, as demonstrated by indirect immunofluorescence. Cells stained by a suitably absorbed rabbit anti-mouse brain serum showed various degrees of fluorescence, from bright fluorescent rings to a few speckles per cell; lymphocytes from the spleen of deprived mice (B mice) predominantly stained in small caps. Double labelling experiments in which B cells were identified by their 'easily detectable' surface immunoglobulin revealed that a great proportion of these cells had two overlapping caps, a large one formed by the anti-immunoglobulin serum and a small one formed by the anti-brain serum. Up to 10 per cent of these spleen B cells, however, appeared as strongly fluorescent as T cells, with the suitably absorbed heterologous anti-brain serum. No anti-immunoglobulin activity was detected in this serum. It is therefore suggested that some B cells may bear on their surfaces a theta or theta-related antigen similar to that on T cells.