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Membrane receptors coupled to GTP binding G-proteins constitute one of the largest families of proteins involved in ligand binding, signal transmission and modulation of physiological effects. A large majority of current pharmaceuticals are actually ligands for this type of receptor, including e.g. the catecholamine, dopamine, serotonin and histamine antagonists. In recent years, an impressive number of the genes encoding these receptors have been cloned, sequenced and expressed in model cell lines. Molecular genetics has thus uncovered the existence of a surprisingly large number of homologous receptor subtypes each capable of binding the same natural ligand, but which may be distinguished on the basis of variable recognition patterns of synthetic ligand panels, variable expression during development and differentiation or different G-protein coupling and effector modulation. We have summarized in Table 1 some of the recently cloned receptors and have attempted to group them according to the type of ligand recognized: non peptidic, peptidic or other, including light and olfactory substances. Further information and references can be found in recent reviews.

A monoclonal antibody against Legionella pneumophila has been produced and characterized. The antibody was of the gamma-3 isotype and recognised the lipopolysaccharides of the bacteria as was confirmed by Western blotting. Preliminary assays were performed for the detection of the antigen in clinical samples in order to set up a rapid laboratory technique for the early diagnosis of legionellosis. By using an immuno-enzymatic technique, less than 30 000 bacteria or corresponding antigens could be detected in a few hours.