Human IgG subclass assays using a novel assay method.

To facilitate assays for human IgG subclasses, we have adapted a novel assay method (particle concentration fluorescence immunoassay) (Jolley et al., 1984; MacCrindle et al., 1985) using one polyclonal and several monoclonal antibodies for human IgG subclasses. The advantages of this new assay over previously described methods are sensitivity (0.3-3 micrograms/ml), and automated measurement of multiple samples in a short time (2 h). We found that a monkey antibody for IgG2 and monoclonal antibodies for IgG1, IgG4b epitope, and IgG3 can be adapted to this method. We evaluated 7 different antibodies to IgG4 without finding a suitable monoclonal antibody for this assay method. Several of these IgG4 hybridoma antibodies, however, could be used in a competitive radioimmunoassay using polyvinyl microtiter plates. The usefulness of a monoclonal antibody to the IgG4b epitope was evaluated because no suitable monoclonal antibodies for IgG2 are available. Because IgG4 levels are usually much smaller than IgG2 levels, and the IgG4b epitope is expressed on all IgG2 alleles and only some IgG4 alleles (Kunkel et al., 1970), the antibody for IgG4b is potentially useful to screen a large number of samples for IgG2 deficiency. However, when the monoclonal antibody for IgG4b was compared with an IgG2 specific antibody produced in a monkey, the IgG4b antibody could identify only about half of the patients with known IgG2 deficiency.

Study of the DBA/2Ha immunodeficiency: X-chromosome mosaicism and in vivo immunoresponses.

DBA/2Ha mice have an X-chromosome-linked immunodeficiency and lack the receptor to a TRF (T cell replacing factor) on a subpopulation of B cells. Their immunodeficiency is considered to resemble that of CBA/N, another X-chromosome-linked immunodeficiency. To facilitate direct comparisons of the two immunodeficiencies and to study the in vivo manifestations of DBA/2Ha immunodeficiency, we measured phenotypes and functions of B cells of DBA/2Ha mice. We found that the expression of sIgM among B cells is normal in DBA/2Ha mice, heterozygous females equally express both affected and normal B cell subpopulations, and DBA/2Ha mice respond well to a TI-2 antigen (TNP-Ficoll) and a polyclonal activator (LPS). Unlike CBA/N, DBA/2Ha mice demonstrate very little in vivo immunodeficiencies.

Subpopulations of B lymphocytes in germinal centers, II. A germinal center B cell subpopulation expresses sIgD and CD23.

To understand B cell development in germinal centers, it is important to delineate the expression of surface antigens among germinal center cells. Because it is unclear whether germinal center cells express common antigens such as sIgD and CD23, we studied their expression among tonsillar lymphocytes with flow cytometry, immunohistochemistry, and in vitro stimulation. Upon studying a large number of tonsils with flow cytometry, we found that occasional tonsils have a very large number of sIgD+ cells among their PNA+ cells. Furthermore, the occasional tonsils with a large number of sIgD+ and PNA+ cells also have many CD23+ cells among their PNA+ cells. Tonsil sections stained immunohistochemically revealed germinal centers containing sIgD+ cells. In addition, PNA- and sIgD+ cells can be induced to express PNA binding sites in vitro without losing the expression of sIgD. Taking these findings together, we conclude that a subpopulation of germinal center B cells coexpresses sIgD and CD23.

Mitogen-induced human IgG subclass expression. II. IgG1 and IgG3 subclasses are preferentially stimulated by a combination of Staphylococcus aureus Cowan I and pokeweed mitogen.

Mitogens generally stimulate human IgG subclass production in amounts proportional to their abundance in serum (IgG1 greater than IgG2 greater than IgG3 greater than IgG4). We report here that a combination of Staphylococcus aureus Cowan strain I and pokeweed mitogen consistently stimulates human peripheral blood lymphocytes in vitro to preferentially produce more IgG1 and IgG3 than IgG2. This preferential stimulation can be measured by increases in the number of immunoblasts (cells with detectable cytoplasmic immunoglobulin) as well as in secreted immunoglobulin. The preferential stimulation pattern is established by the fourth day of culture and is maintained at least until the tenth day. Removal of T cells and subsequent stimulation of B cells with S. aureus Cowan I and interleukin 1 (IL-1) interleukin 2 (IL-2), interleukin 4 (IL-4), or interferon-gamma (IFN-gamma) failed to enhance any IgG subclass production, indicating the requirement for multiple lymphokines in IgG subclass production. The significance of these findings is discussed with respect to B-cell regulatory molecules and the coordinate expression of IgG subclasses.

Dihydropyrimidine dehydrogenase deficiency caused by a novel genomic deletion c.505_513del of DPYD.

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disorder of the pyrimidine degradation pathway. In a patient presenting with convulsions, psychomotor retardation and Reye like syndrome, strongly elevated levels of uracil and thymine were detected in urine. No DPD activity could be detected in peripheral blood mononuclear cells. Analysis of the gene encoding DPD (DPYD) showed that the patient was homozygous for a novel c.505_513del (p.169_171del) mutation in exon 6 of DPYD.

Production, characterization and use of five monoclonal antibodies to human IL-4.

We describe five murine monoclonal antibodies that are specific for human IL-4. At least three spatially distinct epitopes on the hIL-4 molecule are recognized by this panel of antibodies which allowed development of a sensitive sandwich EIA specific for hIL-4. The EIA is capable of detecting 200 pg/ml of hIL-4 and exhibits no detectable crossreactivity to seven other human cytokines examined. In addition to the EIA these antibodies are also useful in a number of other techniques for investigating hIL-4. Recombinant hIL-4 can be easily and efficiently purified by affinity chromatography using these mAbs. Western blotting with two of the antibodies detects as little as 1.8 ng/ml of hIL-4 in a 50 microliters sample. Finally, we present a method for cytoplasmic localization of hIL-4 by a fluorescence staining method utilizing a hIL-4 specific mAb.

Immunologic and clinical status of blood donors with subnormal levels of IgG2.

To determine the immunologic and clinical status of individuals from a general population with subnormal levels of IgG2, we prospectively studied 37 of 312 blood donors with low IgG2 levels identified among 8015 donors. We examined (1) G2m(23) allotypes, (2) levels of other IgG subclasses and immunoglobulin classes, (3) composition of peripheral leukocyte populations, (4) responses to two carbohydrate antigen vaccines, (5) in vitro secretion of IgG subclasses by isolated lymphocytes after mitogen stimulation, and (6) clinical histories. We found that most (90%) individuals with subnormal IgG2 levels had G2m(23)- allotypes, whereas only 30% of the unselected donors had G2m(23)-. When individuals were separated according to their G2m(23) allotype, we found that IgG2 "normal" range for individuals with G2m(23)- allotype is 35% lower than for individuals with G2m(23)+ allotype. Individuals who had G2m(23)- allotype and had IgG2 levels greater than or equal to 0.8 but less than 1.3 gm/L had no other immunologic abnormalities. In contrast, the individuals with G2m(23)+ allotype and with IgG2 levels less than 1.3 gm/L and the individuals with G2m(23)- allotype and with IgG2 levels less than 0.8 gm/L often had additional immunologic abnormalities, including IgA and/or IgG4 deficiency and decreased in vitro expression of IgG2 subclass. None of these individuals had a clinical history remarkable for recurrent infections. Thus, subnormal IgG2 levels interpreted with G2m(23) corrected normal ranges may be a marker of other immunologic abnormalities but taken alone probably have little clinical significance in a general healthy population.

In situ chemical cleavage of proteins immobilized to glass-fiber and polyvinylidenedifluoride membranes: cleavage at tryptophan residues with 2-(2'-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine to obtain internal amino acid sequence.

Proteins immobilized to glass-fiber supports and polyvinylidenedifluoride membranes are cleaved in situ with a tryptophan residue-specific reagent, 2-(2'-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine. Protein fragments can be eluted from polyvinylidenedifluoride membranes after in situ digestion and electrophoresed and electroblotted to new polyvinylidenedifluoride membranes for subsequent sequence determination of selected bands. Five proteins (bovine serum albumin, ovalbumin, beta-casein, beta-lactoglobulin, and myoglobin) of known sequence containing one to three tryptophan residues each were used as model substrates to evaluate the specificity and extent of cleavage. Under the conditions used, the reaction is rapid and exhibits a high degree of specificity for tryptophan residues since N-terminal sequence analysis of the digested, immobilized samples yields the expected, newly generated N-termini. No detectable cleavage occurred at nontryptophan residues nor at acid labile aspartic acid-proline peptide bonds. Solution cleavage reactions were also performed and the resulting digest was analyzed by gel electrophoresis. We found a positive correlation between the solution and in situ cleavage reactions, in that, proteins which show cleavage in the solution reaction also yield internal sequence data after in situ digestion. Since tryptophan occurs with low frequency in proteins, this cleavage reaction has the potential to generate a small number of fragments and in favorable circumstances allow sequence analysis of the unfractionated reaction mixture. In addition, the sequence obtainable after, but not before, in situ digestion can be used as an indication that the N-terminus of the protein is blocked.

Spontaneous secretion of IgG subclasses by intestinal mononuclear cells: differences between ulcerative colitis, Crohn's disease, and controls.

Spontaneous IgG and IgG subclass secretion patterns by isolated intestinal mononuclear cells (MNC) from control and inflammatory bowel disease (IBD) specimens were examined. Intestinal MNC from IBD specimens spontaneously secreted more total IgG than did control intestinal MNC. This increased spontaneous IgG secretion by ulcerative colitis intestinal MNC was primarily due to markedly increased production of IgG1. Slightly increased secretion of IgG3, but not IgG2 by ulcerative colitis intestinal MNC was present when compared with control and Crohn's disease intestinal MNC. In contrast, Crohn's disease intestinal MNC exhibited increased spontaneous secretion of all the IgG subclasses examined, with IgG2 being predominant.