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CD40 ligand (CD40L) is a glycoprotein expressed on the surface of activated helper T cells, basophils, mast cells, and eosinophils. Binding of CD40L to its receptor CD40 on the B cell surface induces B cell proliferation, adhesion, and immunoglobulin class switching. We have identified soluble cleavage products of human CD40L in the supernatant of a stimulated human T cell clone. Subcellular fractionation experiments have shown that the transmembrane CD40L is processed inside the microsomes and that its cleavage is stimulation-dependent. The native human soluble CD40L is trimeric and, when used in conjunction with interleukin-4, induces B cell proliferation.

IN the course of an empirical screening programme we found that culture nitrates of Aspergillus wentii, grown on Raulin–Thom medium (5 per cent glucose) supplemented with 0.1 per cent Difco yeast extract, have a pronounced inhibitory effect on the growth of ‘Meteor’ pea seedlings. When seedlings were sprayed to run-off with undiluted culture nitrate, shoot growth almost ceased for a week and then recommenced slowly. Newly formed internodes were abnormally short; leaflets were very narrow, in extreme cases becoming almost linear; flowers were similarly reduced, being almost apetalous; there was a marked loss of apical dominance, several axillary buds producing dwarfed branches. Newly formed stems and leaves were markedly chlorotic. This abnormal growth persisted throughout the subsequent life of the plants. The leaves sprayed, but not those formed after spraying, developed necrotic spots.

IT has been thought unlikely that antibiotics are produced under natural conditions, (a) because the necessary nutrients would not usually be available and (b) because other micro-organisms might be expected to compete for nutrients and, in some cases, to destroy metabolically any antibiotic formed. Nevertheless, a plant parasite may have access to a relatively rich nutrient supply and may be, in early stages of an infection at least, isolated from the influence of other micro-organisms. Penicillium expansum is an unspecialized plant parasite, causing storage rots of apples; most freshly isolated strains produce the antibiotic patulin (synonyms : clavacin, expansine) in suitable culture media. We thought it of interest to see whether it produces patulin in apple tissues.