Quantitative assay of a human monoclonal IgM antibody (HA-1A) in human serum

A rapid, specific and sensitive radiometric assay was developed capable of quantitating serum levels of HA-1A, a human IgM monoclonal antibody to endotoxin. 'Private' anti-idiotypic murine monoclonal antibodies were produced and utilized in the assay to avoid cross-reactivity with normal human IgG, IgM, IgA, IgE or IgD. The presence of E. coli or gram-negative lipopolysaccharide in the sera did not affect the ability of the assay to detect HA-1A. The sensitivity of the assay was calculated to be 25 ng/ml with an interassay coefficient of variation of less than 10%. In one patient given 100 mg of HA-1A, peak serum concentration was 101.5% of the predicted value with a mean plasma half life of 24.5 h. This assay will be useful in establishing the pharmacokinetics of HA-1A and in monitoring serum levels during phase II and phase III clinical trials.