Recent evidence shows that mature Thy‐1 glycoprotein lacks amino acids 113‐143 predicted from the cDNA sequence and is anchored to the plasma membrane by a phosphatidylinositol‐containing glycolipid attached to amino acid 112. Previously characterized Thy‐1‐deficient mutant lymphoma lines of complementation classes A and E were analysed. They make detergent binding Thy‐1 precursors but, in contrast to wild‐type, the detergent binding moiety cannot be removed by phospholipase C. Moreover, tryptophan which only occurs at position 124 is incorporated into mutant but not parental Thy‐1. This suggests that the mutants make a Thy‐1 precursor of 143 amino acids but fail to replace its C‐terminal end by a glycolipid anchor.

The attachment of glycolipid anchors to the Thy-1 glycoprotein during biosynthesis was followed by the change of detergent-binding properties of biosynthetically labelled Thy-1 precursors upon phospholipase C treatment in the murine thymoma lines BW5147 and S1A. In S1A, 80% of the Thy-1 molecules were phospholipase-C-sensitive after a 2 min pulse with [35S]methionine, indicating that these molecules were already anchored via a glycolipid tail. In BW5147, 47% of the Thy-1 molecules had phospholipase-C-sensitive anchors attached after a 1.5 min labelling and, with longer pulses, this percentage rose to 76%. Tunicamycin did not block the addition of glycolipid anchors, and glycolipid attachment also occurred at 21 degrees C. The findings suggest that the attachment of glycolipid anchors occurs in the rough endoplasmic reticulum.

Recent evidence shows that the mature Thy-1 surface glycoprotein lacks the C-terminal amino acids 113 to 143 predicted from the cDNA sequence and is anchored in the plasma membrane by a complex, phosphatidylinositol-containing glycolipid attached to the alpha-carboxyl group of amino acid 112. Here we studied the biosynthesis of Thy-1 in two previously described and two newly isolated Thy-1-deficient mutant cell lines. Somatic cell hybridization indicated that their mutations affected some processing step rather than the Thy-1 structural gene. The Thy-1 made by mutants of classes C, F, and H bound detergent but, in contrast to wild-type Thy-1, their detergent-binding moieties could not be removed by phospholipase C. In addition, tryptophan, which only occurs in position 124, was incorporated into Thy-1 of these mutants but not of wild-type cells. Last, the Thy-1 of wild-type but not mutant cells could be radiolabeled with [3H]palmitic acid. Together, these findings strongly suggest that mutants of classes C, F, and H accumulate a biosynthetic intermediate of Thy-1 which retains at least part of the hydrophobic C-terminal peptide. The Thy-1 of these mutants remained endoglycosidase H sensitive, suggesting that it accumulated in the rough endoplasmic reticulum or the Cis-Golgi. A different Thy-1 intermediate was found in a class B mutant cell line: the Thy-1 of this mutant was 2 kilodaltons smaller than the Thy-1 of other cell lines, did not bind detergent, and was rapidly secreted via a normal secretory pathway.

Summary A specific IgE‐mediated response was evaluated in twenty‐eight workers exposed to TDI or MDI, with diagnosis of occupational asthma and positive to bronchial provocative challenge. The presence of anti‐diisocyanate IgE was observed in 27% of subjects exposed to TDI and 83% of those exposed to MDI, particularly in individuals who experienced an acute massive exposure. An immediate‐type response to bronchial provocative test was found in 66% of individuals with specific antibodies. Specific IgE are prevalent (91%) in subjects who developed symptoms before 6 years of exposure to isocyanates. The results suggest an association between the presence of specific IgE, early asthmatic symptoms and heavy episodic exposure.

Some parameters which might affect RAST results, i.e. incubation length, degree of ligand substitution, and total IgE levels, were examined in a RAST system employing diphenylmethane diisocyanate--human serum albumin (MDI-HSA) conjugates as antigens, both in exposed symptomatic and in non-exposed subjects. The reaction equilibrium was reached after 9 and 18 h. respectively, in the first and the second step of the test. A marked correlation with the degree of ligand substitution was observed, the highest sensitivity being achieved with the lowest (2.9) MDI/HSA molar ratio examined. Higher (up to 50) degrees of substitution resulted in progressively lower levels of radioactivity bound and in a loss of specificity, as confirmed by RAST inhibition experiments. At high levels of ligand substitution, high titers of total serum IgE affected RAST results.