Specific IgE antibody responses to ragweed allergens Ra5S and Ra5G associated with distinct HLA-DR beta genes.

Previous studies have established that sensitivity (IgE antibody response) to Ra5S, a 5000 mol. wt protein of short ragweed pollen, is significantly associated with host possession of HLA-DR2. The same allele was implicated [Goodfriend et al. (1985) Molec. Immun. 22, 899-906] in sensitivity to Ra5G, a 4400 mol. wt homologue of Ra5S in giant ragweed pollen, based on frequency of co-sensitivity to both proteins. However, data reported here generated in HLA-DR assays of mono-sensitive individuals demonstrate that sensitivity to Ra5S and Ra5G is associated with separate alleles: DR2 and DRw52 respectively. Results consistent with the same sensitivity/DR associations were obtained in immunoabsorption studies with sera from co-sensitive individuals. As HLA-DR2 and DRw52 have identical alpha but different beta chain types (beta 1 and beta 3), it was considered that IgE antibody responses to Ra5S and Ra5G are associated with distinct DR-beta genes.

Ra5G, a homologue of Ra5 in giant ragweed pollen: isolation, HLA-DR-associated activity and amino acid sequence.

Recent studies [Marsh et al. (1982) J. exp. Med. 155, 1439-1451; Coulter (1983) M.Sc. thesis, McGill University, Montreal, Canada; Coulter et al. (1983) in Genetic and Environmental Factors in Clinical Allergy (Edited by Marsh D.G., Blumenthal M.N. and Santilli J., Jr), University of Minnesota Press, Minneapolis, MN] have shown a highly significant association between HLA-Dw2/DR2 and host sensitivity to the 5000-D, 4-disulfide bonded protein Ra5S of short ragweed pollen. To extend these findings, we isolated Ra5G, an Ra5S-like protein, from giant ragweed pollen by gel and ion-exchange chromatography. The protein was homogeneous by polyacrylamide gel electrophoresis (pH 4.3), reverse-phase high-performance liquid chromatography, and antigenic assays. Its mol. wt and amino acid composition (including 8 half-cystine residues) were closely similar to Ra5S, but the two proteins had little or no antigenic or allergenic cross-reactivity. In a study of 200 ragweed-sensitive individuals, host sensitivity simultaneously to Ra5G and Ra5S was significantly associated with the DR2 allele. The amino acid sequence of Ra5G was determined and showed close homology with Ra5S. The potential function of a highly homologous decapeptidyl sequence stretch is discussed in relation to Ir gene control of immune response to the 2 proteins.

Abscisic acid and osmoticum prevent germination of developing alfalfa embryos, but only osmoticum maintains the synthesis of developmental proteins.

Developing seeds of alfalfa (Medicago sativa L.) acquire the ability to germinate during the latter stages of development, the maturation drying phase. Isolated embryos placed on Murashige and Skoog medium germinate well during early and late development, but poorly during mid-development; however, when placed on water they germinate well only during the latter stage of development. Germination of isolated embryos is very slow and poor when they are incubated in the presence of surrounding seed structures (the endosperm or seed coat) taken from the mid-development stages. This inhibitory effect is also achieved by incubating embryos in 10(-5) M abscisic acid (ABA). Endogenous ABA attains a high level during mid-development, especially in the endosperm. Seeds developing in pods treated with fluridone (1-methyl-3-phenyl-5[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone) contain low levels of ABA during mid-development, and the endosperm and seed coat only weakly inhibit the germination of isolated embryos. However, intact seeds from fluridone-treated pods do not germinate viviparously, which is indicative that ABA alone is not responsible for maintaining seeds in a developing state. Application of osmoticum (e.g. 0.35 M sucrose) to isolated developing embryos prevents their germination. Also, in the developing seed in situ the osmotic potential is high. Thus internal levels of osmoticum may play a role in preventing germination of the embryo and maintaining development. Abscisic acid and osmoticum impart distinctly different metabolic responses on developing embryos, as demonstrated by their protein-synthetic capacity. Only in the presence of osmoticum do embryos synthesize proteins which are distinctly recognizable as those synthesized by developing embryos in situ, i.e. when inside the pod. Abscisic acid induces the synthesis of a few unique proteins, but these arise even in mature embryos treated with ABA. Thus while both osmoticum and ABA prevent precocious germination, their effects on the synthetic capacity of the developing embryo are quite distinct. Since seeds with low endogenous ABA do not germinate, osmotic regulation may be the more important of these two factors in controlling seed development.