Jean-Louis Preud'homme

Immunoglobulins on the surface of lymphocytes in fifty patients with primary immunodeficiency diseases

Abstract Surface immunoglobulins were studied by immunofluorescence on the lymphocytes of 50 patients with primary immunodeficiencies. Immunoglobulin-bearing lymphocytes were practically not detectable in sex-linked agammaglobulinemia and in several cases of variable immunodeficiencies with humoral predominance, irrespective of the degree of infection. Normal or increased numbers of lymphocytes carrying immunoglobulins in the absence of the corresponding plasma cells were found in several cases of variable immunodeficiencies, particularly in those with node follicular hyperplasia and during infections, suggesting a block in the maturation of B lymphocytes into plasma cells. Similar results were obtained in selective IgA deficiency and ataxia-telangiectasia whereas the findings in Wiskott-Aldrich syndrome reflected the serum immunoglobulin pattern. Very high numbers of immunoglobulin-bearing lymphocytes were a striking finding in a neonate with severe combined immunodeficiency. The significance of these data with respect to disease pathogenesis and normal immune response is outlined.

Structural and functional properties of membrane and secreted IgD

More than 35 years ago, study of an unknown immunoglobulin (Ig) in the serum from a myeloma patient led to the discovery of IgD. Subsequently, the finding that it also exists as a membrane-bound Ig stimulated a large number of studies during the 70s. Then, the interest on IgD shrank, largely because of the lack of known function of secretory IgD (secIgD) and of a stagnating knowledge of the functions of surface IgD. In the recent years, very significant advances followed the tremendous accumulation of data on the physiology of the B cell receptor, of which IgD is the major component, on the role of secIgD in normal and diseased individuals. This review, which is focused on human IgD but integrates data in the mouse and other species when needed, summarizes present data on the structure, synthesis and functions of both membrane and secIgD, IgD receptors and the involvement of IgD in various diseases, especially the hyperIgD syndrome.

Characterization of jacalin, the human IgA and IgD binding lectin from jackfruit

The lectin jacalin from the jackfruit Artocarpus heterophyllus reacts by precipitation and western blotting with human IgA1 and IgD but not with IgA2 (nor IgG and IgM). However, it weakly binds IgA2 as shown by affinity chromatography and competitive ELISA. Predominantly reactive carbohydrates are D-galactose and N-acetyl D-galactosamine. Jacalin has an apparent Mr of about 54,000 and is probably made up of three non-glycosylated and one glycosylated non-covalently linked subunits. Its electrophoretic properties and amino acid and carbohydrate composition are indicated.

Glomerular and serum immunoglobulin G subclasses in membranous nephropathy and anti-glomerular basement membrane nephritis

The distribution of human IgG subclasses among the glomerular deposits of 53 patients with glomerulonephritis was examined by immunofluorescence (IF) with subclass-specific monoclonal antibodies (Mab). A subclass restriction was observed in idiopathic membranous nephropathy (MN) with glomerular deposits predominantly containing IgG4 (81% of the studied biopsies) and IgG1 (75%). In de novo MN, occurring after transplantation, the restriction was markedly different, with a predominance of IgG1 (100%) and IgG2 (69%). In anti-glomerular basement membrane (a-GBM) nephritis the restriction was considerable with deposits containing almost exclusively IgG1 (91%) and IgG4 (73%). The same restriction was observed for circulating anti-GBM antibodies detected by indirect IF assay. By contrast IgG1, IgG2, and IgG3 deposits were identified in lupus proliferative glomerulonephritis. Serum IgG subclass levels were measured in 29 patients with idiopathic MN and a-GBM nephritis by an indirect competitive immunoenzymatic assay using Mab. Mean percentage of IgG2 serum level was significantly lower in patients. In spite of high variations from patient to patient, a serum IgG subclass imbalance was clearly present in 10 cases with low IgG2 and high IgG1 and IgG3 levels. The imbalance in these patients was not due to urinary loss since it was observed with a similar frequency in hypo- and normoimmunoglobulinemic patients. In 5 out of these 10 patients IgG2 levels were very low, analogous to those observed in selective IgG2 deficiency. Whether the important subclass restriction of glomerular IgG (in which patterns differed according to the type of glomerulonephritis) and the serum subclass imbalances were due to a clonally restricted antibody response to a particular antigen or to a host immune response defect, or both, remains to be elucidated.

Primary structure of a variable region of the VI subgroup (ISE) in light chain deposition disease

Although structural abnormalities of monoclonal immunoglobulin light chains (LC) are suspected to play a determinant role in non‐amyloid light chain deposition disease (LCDD), this condition is as yet poorly documented at the molecular level, since only three sequences have been reported to date. In a case of myeloma‐associated LCDD, the patients urine contained an unglycosylated κ Bence Jones protein made up of dimers and monomers with an apparent molecular mass of 25000 which was assigned to the VκI subgroup by N‐terminal amino acid sequencing. The complete variable region sequence of the monoclonal κ chain produced by the malignant plasma cells was amplified by polymerase chain reaction (PCR) using small amounts of material obtained by bone marrow aspiration. The sequence of three independently amplified cDNA clones derived from a normal‐sized κ messenger RNA was identical to that of the urinary κ chain. The κ mRNA had an overall normal structure made up of a VκI sequence rearranged to JκI‐ Several unusual features of the variable region (the first complete VκI sequence reported in LCDD) included three substitutions that introduced hydrophobic residues at spatially close positions. The strategy associating N‐terminal sequence determination and cDNA cloning by PCR could help in accumulating new sequence data and improving our understanding of LCDD pathogenesis.

Primary structure of a monoclonal κ chain in myeloma with light chain deposition disease

Previous data suggest that structural abnormalities of immunoglobulin light chains may be responsible for non‐amyloid light chain deposition disease (LCDD). We report on the complete primary sequence deduced from complementary (c)DNA analysis of a normal‐sized κ chain in a case of myeloma‐associated LCDD. The patients urine contained a κ type Bence‐Jones protein made of monomers and dimers of an unglycosylated κ chain. The bone marrow myeloma cells contained intracellular κ and γ chains by immunofluorescence. Biosynthesis experiments showed the production of normal‐sized γ chains and of κ chains with the same apparent molecular mass (Mr) in SDS gels as the urinary κ chain (26000–27000). These κ chains were secreted as assembled IgG molecules and as a large excess of free monomers and dimers. The complete sequence of two identical cDNA clones derived from a normal‐sized κ messenger RNA indicated that this K chain belonged to the rare VκIV subgroup. The κ mRNA had an overall normal structure made up of the VκIV sequence rearranged to JκIV and followed by a normal constant exon of the Km(3) allotype. The variable region differed from the VκIV‐JκI germline sequence by 17 amino acid substitutions. The peculiar sequence of the variable region of this κ chain of a rare subgroup might relate lo its tissue deposition.

Jacalin: a lectin mitogenic for human CD4 T lymphoctyes

The major protein component of seeds from jackfruit is the lectin jacalin. Jackfruit crude extracts are known to stimulate human lymphocytes, but the mitogenic properties of purified jacalin have not been studied in detail so far. Study of the proliferative response of cell populations from normal human peripheral blood to purified jacalin showed it to be mitogenic through an interaction with lymphocytes by its lectin‐binding site, as shown by inhibition by IgA. Jacalin failed to stimulate B cells to proliferate and to undergo plasma cell maturation. It induced a proliferation of CD4 (and not CD8) lymphocytes, as shown by phenotypic analysis of cells recovered after culture and by studies of the response of isolated T cell subpopulations. The proliferative response to jacalin was autologous monocyte‐dependent. The kinetics of jacalin‐induced DNA synthesis, expression of CD25 and interleukin‐2 secretion was shifted by comparison with that induced by phytohaemagglutinin. The reason for the restricted responsiveness of CD4T cells is presently unclear; jacalin bound to all blood cells and did not significantly co‐cap with CD1, CD2, CD3, CD4, CD8 and CD38, and jacalin response was neither enhanced nor inhibited by antibodies to these surface antigens.

Serum IgG subclass levels in patients with primary immunodeficiency syndromes or abnormal susceptibility to infections.

Serum IgG subclass levels were measured using an indirect competitive immunoenzymatic assay with monoclonal antibodies in 221 patients affected with definite immunodeficiency (ID) syndromes and 229 patients presenting with infection patterns suggestive of ID, but with normal immunoglobulin class levels and no clear evidence of ID. In common variable ID and IgG-IgA deficiency with normal or high IgM, subclass imbalance (mostly IgG1-IgG3 or IgG2-IgG4 deficiency) was the rule, with a higher incidence of severe infections in IgG2-IgG4 defects. One-fifth of patients with IgA deficiency, especially those with autoimmune cytopenia, had subclass deficiencies with no significant correlation with the occurrence of infections. Subclass (mostly IgG2-IgG4) deficiencies were also observed in severe combined ID, defective expression of HLA class II antigens, chronic mucocutaneous candidiasis, and IgM deficiency. Subclass levels were normal in all but one (who was IgG3 deficient) patient with the Wiskott-Aldrich syndrome and in the Buckleys syndrome, except for an unusual patient who presented with low IgG and IgA levels. Subclass (mainly IgG2) deficiency occurred in 24% of infected patients without known ID.

Jacalin, the human IgA1 and IgD precipitating lectin, also binds IgA2 of both allotypes.

The lectin jacalin from jackfruit seeds shows a human IgA-subclass specificity by gel precipitation and Western blotting. However, its reactivity with IgA2 is a matter of controversy. We further studied the immunoglobulin isotype specificity of jacalin by affinity chromatography with myeloma sera and by inhibition of jacalin binding to solid-phase IgA1 by purified monoclonal immunoglobulins. The lectin proved to bind IgA2 of both allotypes with a lower apparent affinity than for IgA1 and IgD.

Evaluation of monoclonal antibodies with specificity for human IgA, IgA subclasses and allotypes and secretory component. Results of an IUIS/WHO collaborative study.

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.