Human anti-acetylcholine receptor antibodies use variable gene segments analogous to those used in autoantibodies of various specificities

The production of autoantibodies to the nicotinic acetylcholine receptor are responsible for many of the neurological symptoms observed in myasthenia gravis. An understanding of the structural organization of the anti-receptor antibodies may help to define the role of these antibodies in the pathogenesis of this disease. The nucleotide sequences of the heavy and light chains of three human monoclonal anti-receptor antibodies isolated from peripheral blood lymphocytes from two patients with myasthenia gravis were analyzed. In addition, the structure of an anti-idiotypic antibody was studied. The V_H and V_L gene segments used in the anti-receptor antibodies appear to be derived from the same repertoire as gene segments that have been found in other autoantibodies isolated from patients with various autoimmune diseases. The IgM anti-receptor antibodies are direct copies of germline gene segments, while the structures of the IgG anti-receptor antibody and the anti-idiotypic antibody appear to be mutated suggesting that they have undergone antigenic selection.     

The incorporation of iodine in thyroid hormone may stem from its role as a prehistoric signal of ecologic opportunity: an evolutionary perspective and implications for modern diseases

To optimize fitness under conditions of varying Darwinian opportunity, organisms demonstrate tremendous plasticity in their life-history strategies based on their perception of available resources. Higher-energy environments generally promote more aggressive life-history strategies, such as faster growth, larger adult size, greater genetic variation, shorter lifespan, larger brood sizes, and offspring ratio skewed towards the larger-sized gender. While numerous mechanisms regulate life-history plasticity including genetic imprinting, methylation, and growth factors, evidence suggests that thyroid hormone plays a central role. Given the pivotal adaptive role of thyroid hormone, the teleology of its dependence on dietary iodine for production remains unexplained. We hypothesize that iodine may have emerged as a substrate for production of thyroid hormone in prehistoric ecosystems because the former represented a reliable proxy for ecologic potential that enabled the latter to modulate growth, reproduction, metabolic rate, and lifespan. Such a scenario may have existed in early marine ecosystems where ocean-surface vegetation, which concentrates iodine for its antimicrobial and antioxidant properties, formed the basis of the food chain. Teleologic parallels can be drawn to the food-chain accumulation of antimicrobials that also exhibit antioxidant properties and promote adult size, brood size, and offspring quality by modulating central hormonal axes. As each higher species in the food chain tunes its life-history strategy based on iodine intake, the coupling of this functional role of iodine with its value as a resource signal to the next member of the food-chain may promote runaway evolution. Whereas predators in prehistoric ecosystems successfully tuned their life-history strategy using iodine as a major input, the strategy may prove maladaptive in modern humans for whom the pattern of iodine intake is decoupled from resource availability. Iodine acquired through sodium iodide supplementation may independently contribute to some biologic dysfunctions currently attributed to sodium.     

In vitro regulation of thyroglobulin (Tg) autoantibody production by Tg-specific T-cell lines and hybridomas.

To define the interactions between self thyroglobulin (Tg)-reactive T and B we co-cultured enriched B cells taken from rat or mouse Tg-primed mice with major histocompatibility complex (MHC) class II-restricted T-cell lines specific for iodinated determinants on self-Tg, or hybridomas derived from those lines. Using two clonally distinct T-cell hybridomas, ADA2 and CH9, in vitro help for Tg autoantibody responses was observed using mouse (M)Tg-primed B cells and a 100 ng/ml MTg challenge. Using rat Tg-primed B cells and the same conditions, only CH9 provided help, indicating that the fine specificity of B cells influences their ability to interact with specific anti-Tg T-cell clones. In contrast to T-cell hybridomas, their parent T-cell lines MTg9B3 and MTg12B suppressed Tg autoantibody responses in vitro, although they augmented bystander proliferation of unprimed B cells. The MTg12B cells also (i) diminished the survival of Tg-primed B cells, and (ii) inhibited the proliferation of an antigen-presenting B-cell hybridoma (LK35.2) in a cytostasis assay. These findings together support the view that their suppressive activity is mediated through cytotoxicity. While the role of class II-restricted cytotoxic cells in thyroid autoimmunity is unknown, the results suggest that such cells may act to suppress autoantibody responses as well as to mediate tissue damage to class II-expressing thyroid cells.     

Ability of bacteria associated with chronic inflammatory disease to stimulate E-selectin expression and promote neutrophil adhesion.

Porphyromonas gingivalis, Pseudomonas aeruginosa, and Helicobacter pylori have been shown to be associated with adult periodontal disease, chronic lung infections, and peptic ulcers, respectively. The ability of these bacteria to stimulate E-selectin expression and promote neutrophil adhesion, two components necessary for the recruitment of leukocytes in response to infection, was investigated. Little or no stimulation of E-selectin expression was observed with either P. gingivalis or H. pylori when whole cells, lipopolysaccharide (LPS), or cell wall preparations added to human umbilical cord vein endothelial cells were examined. P. aeruginosa was able to induce E-selectin to near-maximal levels; however, it required approximately 100 to 1,000 times more whole cells or LPS than that required by E. coli. Neutrophil-binding assays revealed that LPS and cell wall preparations obtained from these bacteria did not promote endothelial cell adhesiveness by E-selectin-independent mechanisms. In addition, P. gingivalis LPS blocked E-selectin expression by LPS obtained from other bacteria. We propose that lack of E-selectin stimulation and the inability to promote endothelial cell adhesiveness are two additional indications of low biologically reactive LPS. We suggest that this property of LPS may contribute to host tissue colonization. In addition, the ability of P. gingivalis to inhibit E-selectin expression may represent a new virulence factor for this organism.     

Collagens synthesized in vitro by diploid fibroblasts obtained from chronically inflamed human connective tissue

Collagen synthesis by fibroblasts obtained from healthy and diseased human gingiva was compared. The cells were labeled with radioactive amino acids and the collagenous proteins synthesized were characterized after NaCl fractionation by CM-cellulose chromatography and cyanogen bromide peptide analysis. Fourteen cell lines, six from healthy gingiva, six from gingiva with chronic inflammatory periodontitis, and two from acutely inflamed gingiva were studied. All of the cell lines synthesized predominantly type I collagen. Type III collagen was a minor product of all cell lines except one from diseased tissue. Five of six cell lines from diseased gingiva and two of two from acutely inflamed tissue synthesized a collagen that was soluble in 2.5 M NaCl. The alpha1/alpha2 ratio and cyanogen bromide peptide pattern indicated that this fraction contained a collagen of the type alpha1[I]3. The alpha1[I]3 collagen was not detectable in the fibroblast lines obtained from healthy gingiva. It appears that inflamed human gingivae contain fibroblasts which differ phenotypically from cells from normal tissue in that they are capable of synthesizing alpha1[I]3 collagen.     

A modified human ELISPOT assay to detect specific responses to primary tumor cell targets

Background  

The desired outcome of cancer vaccination is to induce a potent T cell response which can specifically recognize and eliminate autologous tumor cells in vivo. Accordingly, immunological assays that demonstrate recognition of native tumor cells (tumor-specific) may be more clinically relevant than assays that demonstrate recognition of tumor protein or peptide (antigen-specific).     

Outbreak ofPneumocystis carinii pneumonia in a renal transplant unit

The charts for seven renal transplant recipients who developedPneumocystis carinii pneumonia were reviewed. They included six men and one woman transplanted a mean of 150 days before the diagnosis of this infection. Six presented at least one episode of acute graft rejection. Cytomegalovirus pneumonia was diagnosed in six of the patients. All patients were treated with cotrimoxazole. Global mortality was 43 %. In additional to the classic hypothesis of latentPneumocystis carinii reactivation in immunocompromised hosts, this and previous reports of outbreaks strongly suggest either a person-to-person transmission or acquisition from the environment. Molecular typing of isolates could be of value in identifying the source of such outbreaks. Chemoprophylaxis should be more systematically administered to renal transplant patients, co-trimoxazole being the drug of choice.     

Amino acid sequences of myosin essential and regulatory light chains from two clam species: Comparison with other molluscan myosin light chains

Summary We have determined the amino acid sequences of the essential light chains (ELC) and regulatory light chains (RLC) of myosin from two species of clam,Mercenaria mercenaria andMacrocallista nimbosa, using protein chemistry methods. The N-termini of all four proteins were blocked, and sequencing was carried out on various chemically and enzymatically produced peptide fragments. Cleavage of eitherMercenaria RLC (MRLC) orMacrocallista RLC (VLC) at its 3 Arg yielded four peptides, three of which could not be sequenced directly, due to an N-terminal blocking group and 2 Arg-Gln bonds in these proteins. The fourth peptide was partially and specifically cleaved at an unusually reactive residue, Met-64, which is invariant in all known RLC sequences. A comparison of all available molluscan ELC and RLC sequences was carried out in search of clues to functionally important features of these proteins in muscles which are regulated by a Ca²⁺-sensitive myosin. By analogy with other RLCs, VRLC and MRLC may be phosphorylated at Ser-11 by an endogenous kinase. All myosin light chains, like troponin C and calmodulin, contain four homologous regions, I to IV, each of which contains a twelve-residue potential Ca²⁺-binding loop flanked on either side by a pair of helices. All RLCs, including those from Ca²⁺-insensitive myosins, contain a divalent cation-binding site in region I. Clam and other molluscan ELCs contain a single Ca²⁺-binding site in region III. This site is present only in the ELCs of myosins that are regulated by direct binding of Ca²⁺. The ELC site III is likely to play a key role in the regulation of molluscan muscle contraction.     

Seroprevalence of anti-HIV antibodies in a rural Haitian population

A sero-epidemiological study was conducted from July to August 1988, in a haitian population living in rural area. Out of 116 serum samples searched for H1V1 antibodies and anti-HTLV1, 5.2% and 4.3% were reactive, respectively. Both positivity H1V1/HTLV1 was observed in one case. HBs Ag carriers were 13%. Analysis of seroreactive people in this population enhances the epidemiological trends of AIDS in Caribbean (rural spreading, heterosexual transmission, sex ratio levelling) which relate to african type AIDS.