Membrane immunoglobulin-cytoskeletal interactions--II. Biochemical analysis of cytoskeletally associated IgM.
In a previous paper [Albrecht and Noelle, J. Immun. 141, 3915 (1988)], biochemical and flow cytofluorometric analysis revealed a 78,000 mol. wt cell surface protein that was constitutively associated with the detergent-insoluble fraction (cytoskeleton) of B lymphocytes. The identity of this band was serologically confirmed as IgM and was therefore referred to as cyto-IgM. Since cyto-IgM may play an integral role in mIgM-cytoskeletal interactions, the molecular nature of cyto-IgM was investigated. In its non-reduced form, cyto-IgM was pentameric. Treatment with endoglycosidase F revealed an Ig heavy chain with a mol. wt of 66,000, which was identical to secreted IgM. The cell surface location of cyto-IgM was independently verified by its sensitivity to protease digestion in intact cells. Conditions which eluted cytophilic Ig from the cell surface did not displace cyto-IgM. Cyto-IgM was present in resting B lymphocytes but absent in neonatal cells. The function of cyto-IgM is discussed in the light of these results.
Albrecht
D L
DL
Graduate Program in Biochemistry, Dartmouth Medical School, Hanover, NH 03756.
Noelle
R J
RJ
D000818:Animals; D000831:Animals, Newborn; D001402:B-Lymphocytes / Q000276:immunology*; D002462:Cell Membrane / Q000276:immunology; D003599:Cytoskeleton / Q000276:immunology*; D007075:Immunoglobulin M / Q000032:analysis*; D051379:Mice; D008811:Mice, Inbred DBA; D008970:Molecular Weight
D007075:Immunoglobulin M