Mixed Enzyme‐Linked Immunosorbent Assay (MELISA) for HLA Class I Antigen: a Plasma Membrane Marker

This study introduces a simple, reproducible assay for HLA class I antigen using antibodies against β2‐microglobulin and the heavy chain on HLA. The sandwich technique was named mixed enzyme‐linked immunosorbent assay (MELISA), and was designed for identification of plasma membranes in neutrophil subcellular fractions. The subcellular localization of HLA was identical to that of other plasma membrane markers, [3H]concanavalin A and detergent‐independent alkaline phosphatase, and was unchanged by stimulation of cells by weak and strong secretagogues. In addition to the presence as part of the HLA complex in the plasma membrane uncomplexed β2‐microglobulin is present in the specific granules of neutrophils. However, the release of β2‐microglobulin from intact neutrophils stimulated with formyl‐methionylleucyl‐phenylalanine was much higher than could be explained by exocytosis of specific granules. Subcellular fractionation studies demonstrated that β2‐microglobulin is localized in fractions characterized by latent alkaline phosphatase and released from this novel secretory compartment in response to stimulation with formyl‐methionylleucylphenylalanine.