IgM cryoprecipitation and anti-immunoglobulin activity in dysgammaglobulinemia type I

Mutations in activation-induced cytidine deaminase in patients with hyper IgM syndrome

Recent studies have shown that mutations in a newly described RNA editing enzyme, activation-induced cytidine deaminase (AID), can cause an autosomal recessive form of hyper IgM syndrome. To determine the relative frequency of mutations in AID, we evaluated a group of 27 patients with hyper IgM syndrome who did not have defects in CD40 ligand and 23 patients with common variable immunodeficiency. Three different mutations in AID were identified in 18 patients with hyper IgM syndrome, including 14 French Canadians, 2 Lumbee Indians, and a brother and sister from Okinawa. No mutations were found in the remaining 32 patients. In the group of patients with hyper IgM syndrome, the patients with mutations in AID were older at the age of diagnosis, were more likely to have positive isohemagglutinins, and were less likely to have anemia, neutropenia, or thrombocytopenia. Lymphoid hyperplasia was seen in patients with hyper IgM syndrome and normal AID as well as the patients with hyper IgM syndrome and defects in AID.

Hyper IgM syndrome associated with defective CD40-mediated B cell activation

Recent studies show that most patients with X-linked hyper IgM syndrome have defects in the gene for CD40 ligand. We evaluated 17 unrelated males suspected of having X-linked hyper IgM syndrome. Activated T cells from 13 of the 17 patients failed to bind a soluble CD40 construct. In these patients, the sequence of CD40 ligand demonstrated mutations. By contrast, T cells from the remaining four patients exhibited normal binding to the CD40 construct. Sequencing of the cDNA for CD40 ligand from these patients did not show mutations. The possibility that hyper IgM syndrome in these four patients was due to abnormalities in the B cell response to CD40-mediated signals was examined. Peripheral blood lymphocytes were stimulated with anti-CD40 alone, IL4 alone or anti-CD40 plus IL4. In comparison with B cells from controls or patients with hyper IgM syndrome and mutant CD40 ligand, B cells from the patients with hyper IgM syndrome and normal CD40 ligand were defective in their ability to secrete IgE (P < 0.02) or express activation markers, CD25 and CD23 (P < 0.02) in response to stimulation with anti-CD40. The failure of these B cells to respond to CD40-mediated activation could not be attributed to a generalized deficiency in B cell activation because IL4 induced normal up-regulation of CD23 and CD25 expression. These findings indicate that hyper IgM syndrome may result from defects in expression of CD40 ligand by activated T cells or defects in CD40-mediated signal transduction in B cells.

CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome

The ligand for CD40 (CD40L) is a membrane glycoprotein on activated T cells that induces B cell proliferation and immunoglobulin secretion. Abnormalities in the CD40L gene were associated with an X-linked immunodeficiency in humans [hyper-IgM (immunoglobulin M) syndrome]. This disease is characterized by elevated concentrations of serum IgM and decreased amounts of all other isotypes. CD40L complementary DNAs from three of four patients with this syndrome contained distinct point mutations. Recombinant expression of two of the mutant CD40L complementary DNAs resulted in proteins incapable of binding to CD40 and unable to induce proliferation or IgE secretion from normal B cells. Activated T cells from the four affected patients failed to express wild-type CD40L, although their B cells responded normally to wild-type CD40L. Thus, these CD40L defects lead to a T cell abnormality that results in the failure of patient B cells to undergo immunoglobulin class switching.

Amino acid sequence of a light chain variable region of a human rheumatoid factor of the Wa idiotypic group, in part predicted by its reactivity with antipeptide antibodies

Antipeptide antisera were raised to the second and third complementarity-determining regions of the light chain derived from a human monoclonal IgM (Sie) which had antigammaglobulin activity and belonged to the Wa cross-reactive idiotypic group of human rheumatoid factors, two of whose members (Sie, Wo1) had been previously sequenced in our laboratory (Andrews and Capra, Biochemistry 20, 5816-5822, 1981). These antisera were found to react with the light chain of another human monoclonal IgM (Go1) that shared the Wa idiotype while antipeptide antisera made to the third CDR of the Sie heavy chain failed to react. The amino acid sequence of the variable region of the Go1 light chain was found to be highly homologous to the light chain of Sie from which the synthetic peptides were derived, particularly in the framework regions and the second and third CDR. This study illustrates that antipeptide antisera are valuable and specific probes for determining the relationship between molecules which exhibit similar antigen binding or idiotypic specificities and, furthermore, such antisera are able to predict amino acid sequences with surprising precision.

Dissection of the human antigammaglobulin idiotype system with monoclonal antibodies

Murine monoclonal antibodies (MoAb) were prepared by immunizing mice with human monoclonal rheumatoid factors from patients with mixed cryoglobulinaemia. Indirect solid phase radioimmunoassay and haemagglutination inhibition were used to screen the MoAb. Reactivity patterns of MoAb were determined using (a) polyclonal and monoclonal IgM proteins, (b) monoclonal IgM proteins from patients with neuropathy, (c) monoclonal and polyclonal IgM antigammaglobulins, and (d) various isolated VkIIIb-positive immunoglobulins. Several patterns were obtained: MoAb reacting with private idiotypic determinants, with VkIIIb-related determinants, and with cross-reactive idiotypes (CRI). Two MoAb of the second type reacted with VkIIIb-positive immunoglobulins and light chains regardless of their antigenic activity. Another MoAb reacted with VkIII light chains only when in association with mu heavy chains. MoAb of the third type defined distinct CRI systems. One of these was restricted to antigammaglobulins and another also involved neuropathy-associated monoclonal IgM proteins. All MoAb clearly reacted with a minor population of normal polyclonal IgM, except for the MoAb detecting private idiotypic determinants. Studies using inhibition of binding by enzyme-linked immunosorbent assay showed that polyclonal IgM antigammaglobulins may carry a CRI determinant detected by one of the MoAb. This CRI system, defined by the MoAb Glo 86.3, was similar to but not identical with the previously described Wa CRI, which is widely prevalent among IgM antigammaglobulins of rheumatoid arthritis.

Cryoglobulinemia

A large number of disease states are characterized by cryoglobulinemia. Quantification and immunochemical classification of cryoglobulins in serum provide information of diagnostic and pathophysiologic utility. Thus, type I cryoglobulins consist of a monoclonal immunoglobulin of a single class and are associated with lymphoproliferative disorders, such as multiple myeloma. Type II (mixed) cryoglobulins contain monoclonal IgM or rheumatoid factor and polyclonal IgG, and occur in patients with Waldenstrom's macroglobulinemia or chronic active hepatitis, for example. In type III cryoglobulins, both the IgM and rheumatoid factor and the IgG components are polyclonal. A large number of autoimmune or infectious diseases exhibit type III cryoglobulinemia. In certain well-studied situations, type II and type III cryoglobulins have been shown to contain antigen-antibody complexes directly involved in tissue injury in vivo, e.g., DNA and anti-DNA in systemic lupus erythematosus.