Distribution of ‘Free’ and HLA‐associated Human β2‐Microglobulin in Some Plasma Membranes and Biological Fluids

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Abstract
The distribution of free and HLA-associated human .beta.2-microglobulin (.beta.2m) in serum, urine, spinal fluid, parotid duct saliva, seminal fluid, amniotic fluid and whey and in membranes from thrombocytes, lymphocytes, neutrophils and fat globules from milk was studied by crossed radioimmunoelectrophoresis (CRIE). The hydrophobic domain of HLA was demonstrable in charge-shift CRIE and by binding to phenyl-Sepharose in hydrophobic-interaction CRIE. In lectin-affinity, CRIE with concanavalin A and Lens culinaris lectin Sepharose the carbohydrate moiety present on HLA exhibited heterogeneity as judged by the appearance of 2 partly separated protein peaks. Except for isolated fat globule membranes, HLA-associated .beta.2m was present on all cells investigated. Free .beta.2m did ot contain a hydrophobic domain as assessed by charge-shift and hydrophobic-interaction CRIE. All body fluids contained .beta.2m in its free form only. In serum, besides the free .beta.2m, 2% was present as HLA-associated .beta.2m, which did not contain a hydrophobic domain. A degradation product of free .beta.2m, with .alpha.-mobility, was observed in sera from patients with malignant disorders, rheumatoid arthritis or systemic lupus erythematosus.