In vitro characterization of a monoclonal IgG(kappa) from a patient with planar xanthomatosis.
OBJECTIVE
To characterize a monoclonal IgG(kappa) (MAb) from a patient with planar xanthoma that precipitated with serum lipids at reduced temperature.


METHODS
The molecular weight (Mr), sensitivity to proteases, and glycosylation of the purified MAb were analyzed. The specificity of the MAb was tested by measuring cryoprecipitation with pure high- (HDL) and low-density (LDL) lipoproteins. The effect of choline, phosphocholine, and glycerol 3-phosphate on the precipitation temperature of LDL by the MAb was studied.


RESULTS
The MAb was larger than normal IgG due to hyperglycosylation of the MAb light chain. It formed cryoprecipitates with pure HDL and LDL as well as the lipids extracted from these lipoproteins. Fab fragments of the MAb lowered the temperature of its precipitation with LDL. Choline, phosphocholine, and glycerol 3-phosphate also lower the precipitation temperature.


CONCLUSIONS
This is the first human IgG reported with apparent specificity for phosphocholine antigens. Its precipitation with lipids at reduced temperature suggests that it recognizes conformations of phospholipid head groups that develop below core body temperature.
Horne
McDonald K
MK
Hematology Service, Department of Laboratory Medicine, W.G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD, USA. mcdonald.horne@gmail.com
Merryman
Paula
P
Cullinane
Ann
A
Remaley
Alan T
AT
D000911:Antibodies, Monoclonal / Q000276:immunology; D008076:Cholesterol, HDL / Q000302:isolation & purification; D008078:Cholesterol, LDL / Q000302:isolation & purification; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D066298:In Vitro Techniques; D014973:Xanthomatosis / Q000276:immunology*
D000911:Antibodies, Monoclonal; D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D007074:Immunoglobulin G