Relationship between mouse lymphocyte receptors for peanut agglutinin (PNA) and Helix pomatia agglutinin (HPA)

The relationship between mouse lymphocyte receptors for peanut agglutinin (PNA) and Helix pomatia agglutinin (HPA) has been investigated by immunofluorescence (cocapping) and radiolabeling. In neuraminidase-treated and untreated thymocytes there are two groups of glycoproteins which bind roughly equivalent amounts of PNA. One group also carries all the detectable receptors for HPA, the other binds only PNA. Binding inhibition experiments suggest that PNA and HPA receptors are in close proximity on the shared glycoproteins. The same two groups of receptors are present on 35-40% of neuraminidase-treated spleen lymphoid cells, mainly immunoglobulin (Ig)-negative lymphocytes. Almost all B cells have only PNA-specific receptors. Five-12% of the untreated spleen cells appreciably bind PNA and only a few bind HPA. Solubilized glycoproteins specific for PNA or HPA were compared by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography. The major PNA-specific radioiodinated glycoproteins of neuraminidase-treated thymocytes, as isolated by affinity chromatography, consist of the 185-kDa and 195-kDa components of the T200 antigen and of two (diffuse) components of about 140 and 120-125 kDa. All these molecules also bind to HPA-Sepharose, with the exception of the 185 kDa component, which is probably the main constituent of the "pure" PNA receptors on the intact thymocytes. In gels directly labeled with radioactive lectins, the only band strongly labeled by PNA and HPA is the diffuse 140-kDa band. The band at 120 kDa is well labeled by PNA, but all the other components are weakly labeled. The mobility of the 140- and 120-kDa bands depends strongly on neuraminidase-treatment. These bands cannot be detected in gels of untreated thymocytes, but a major HPA-and PNA-specific band of lower molecular weight can be labeled after treating the gels with neuraminidase. The factors determining the differences in labeling pattern obtained by different methods as well as the nature of PNA and HPA binding sites are discussed. The same major PNA- and HPA-binding glycoproteins (apart from minor differences) are present on neuraminidase-treated Ig-negative spleen lymphocytes. The major PNA-binding protein of B lymphocytes appears to correspond to the 225-kDa ("B220") antigen specific for these cells.