Preparation and characterisation of an antiserum to the mouse candidate for immunoglobulin D

ANALYSIS of mouse B-lymphocyte surface immunoglobulin (Ig) by isotopic labelling techniques reveals little, if any, IgA or IgG. Instead, the surface Ig consists of monomeric IgM and an Ig similar in physicochemical properties to human IgD 1–3 . In the absence of sequence comparison between human IgD and its assumed mouse counterpart, this assignment is tentative. With this proviso, however, and for the sake of clarity in presentation, we refer to this immunoglobulin as IgD. During development, IgM-bearing cells are the first to arise and the ratio of IgM–IgD determined with labelled adult lymphocytes is higher in the spleen than in lymph nodes or Peyer's patches 1,4 . These findings, however, give the total yield of the two Ig classes and not their distribution on individual lymphocytes. On the basis of the absence of immunoglobulins other than IgM or IgD on the surface of B lymphocytes, we indicated the presence of cells bearing IgM or IgD, or IgM and IgD in mouse spleen cell suspensions 5,6 . In these experiments, IgM was first capped with rhodamine-labelled anti- μ and subsequent ring staining with fluorescein-labelled anti-Fab in the presence of sodium azide was taken as evidence for the presence of IgD. We report here the preparation of an antibody specific for mouse IgD, and its use in the characterisation of mouse B-lymphocyte surface Ig.