Manipulation of isoprenoid biosynthesis as a possible therapeutic option in mevalonate kinase deficiency.

OBJECTIVE: In cells from patients with the autoinflammatory disorder mevalonate kinase (MK) deficiency, which includes the hyperimmunoglobulin D with periodic fever syndrome, MK becomes the rate-limiting enzyme in the isoprenoid biosynthesis pathway. This suggests that up-regulation of residual MK activity in these patients could be a way in which to prevent or alleviate the associated symptoms. We studied the effect of 2 specific inhibitors of isoprenoid biosynthetic enzymes on the residual activity of MK in cells from patients with MK deficiency. METHODS: Skin fibroblasts from MK-deficient patients and from controls were cultured for 7 days with either simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, or zaragozic acid A, an inhibitor of squalene synthase. Following culture, MK activity, MK protein levels, MVK messenger RNA levels, and the effect on the pathway flux toward non-sterol isoprenoid biosynthesis were determined. RESULTS: Treatment of the fibroblasts with either of the inhibitors led to a marked increase in residual MK enzyme activity, which was largely attributable to increased MVK gene transcription. This effect was even more pronounced when the cells were cultured in lipoprotein-depleted medium. The flux toward nonsterol isoprenoid end-product synthesis was reduced when cells were treated with simvastatin but was partly restored by concomitant treatment with zaragozic acid A. CONCLUSION: Our results indicate that manipulations of the isoprenoid biosynthesis pathway that promote the synthesis of nonsterol isoprenoids may provide an interesting therapeutic option for the treatment of MK deficiency.

Relationship between humoral immunoaugmenting properties of DHEAS and IgD-receptor expression in young and aged mice.

IgD-receptors are associated with augmented antibody production in vivo and are induced on CD4+ T cells by aggregated IgD in young but not in aged mice. In the current study orally or intraperitoneally administered DHEAS was found to enhance antibody production, as measured in a plaque-forming cell assay, and also to cause an increased expression of IgD-R on T cells in both young and aged mice. IgD-R+ T cells are enumerated by rosette cell formation with IgD-coated SRBC. Since, as shown previously, the immunoaugmenting effect of IgD-R+ T cells is blocked by injection of monomeric IgD, the effect of monomeric IgD was also examined in DHEAS-pretreated mice. The inhibitory effect obtained with monomeric IgD in these studies indicates that upregulation of IgD-R by DHEAS plays an important role in the immunoenhancing effect of this hormone. In addition, no significant effect of DHEAS was obtained on contact hypersensitivity to DNCB or on proliferative responses of T cells from young or aged mice. Aged but not young mice showed increases in the numbers of Ia+ epidermal Langerhans cells after DHEAS treatment.

Identification of a dog IgD-like molecule by a monoclonal antibody.

IgD has not been identified in dogs. We produced a monoclonal antibody (mAb) designated 9B during the production of hybridomas to dog IgE. Using Western blot analysis under non-reducing conditions, the mAb (9B) recognized a predominant protein band of 185 kDa which was also recognized by anti-dog IgG F(ab')2, suggesting that this 185 kDa protein is an immunoglobulin (Ig) containing light chains. Under reducing conditions, the mAb (9B) recognized only one protein band of 55 kDa which presented a distinct molecular weight (MW) and immunoreactivity from the dog tau, mu, alpha, and epsilon chains. The 55 kDa band did not react with anti-dog IgE, IgM, IgA, and IgG, but did react with the mAb (9B). The MW was 75 kDa for the epsilon chain, 77.5 kDa for the mu chain, 58 kDa for the alpha chain, and 52 kDa for the tau chain. Further, by immunofluorescent staining, this Ig recognized by the mAb (9B) was found on the surface of dog lymphocytes. Studies of this dog Ig with the mAb revealed that this Ig bound to protein A and protein G-Sepharose, and that its enzyme-linked immunosorbent assay (ELISA) activity as measured by the mAb (9B) did not change after heating at 56 degrees C for 2 h. Ragweed-specific IgG, IgE, and this newly defined Ig significantly increased when dogs were immunized with ragweed extract. These data suggest that this Ig is a previously unrecognized IgD-like molecule in dogs.

Two new proteins preferentially associated with membrane immunoglobulin D.

The IgM and IgD classes of antigen receptor can perform different functions on B cells. However, so far no class-specific components communicating with the cytoplasm have been found in the two antigen receptors. We have employed a new biotinylation protocol to search for intracellular membrane Ig-associated proteins. Here we describe two proteins of 29 and 31 kDa that are associated with membrane IgD and to some extent with membrane IgM. The membrane IgM molecule is associated specifically with three proteins of 32, 37 and 41 kDa. The purification and sequencing of the two mIgD-associated proteins revealed that they are novel proteins which are related to each other. These proteins may be the missing link between the antigen receptor and the cytoskeleton and may contribute to functional differences between membrane IgM and membrane IgD.

IgD in human colostrum.

Simultaneous colostrum (C) and plasma samples (P) from 14 women, 1 to 5 days postpartum, were examined. Total IgD and specific IgD antibodies to beta-lactoglobulin, bovine serum albumin, Bermuda grass, and alpha-gliadin were measured by solid phase radioimmunoassay. The geometric mean concentrations of IgD were 35.8 (range 2.2-410) micrograms/dl for colostrum and 591.3 (range 72-4100) micrograms/dl for plasma. Six subjects had a specific IgD antibody C/P ratio more than 10-fold greater than the total IgD C/P ratio, suggesting enhancement of antibody to a specific antigen in the mammary gland. All six had C/P ratios suggestive of local enhancement of IgD antibody to Bermuda grass, and two met this criterion for enhancement of IgD antibodies to beta-lactoglobulin, bovine serum albumin, or alpha-gliadin. Specimens for these studies were obtained during the peak grass pollen season. Seventeen additional subjects were studied to compare total IgD in colostrum and plasma with total IgG and serum albumin. The mean C/P ratio for IgD (0.055 +/- 0.015) exceeded the C/P ratio for total IgG (0.015 +/- 0.003) or total albumin (0.020 +/- 0.002). For 14 of 17 subjects the colostrum/plasma ratio for IgD exceeded the C/P ratio for albumin or IgG. Data were transformed logarithmically and correlation coefficients calculated. For albumin versus IgG in colostrum, there was a strong correlation, r = 0.865, p = 0.001. This was different from albumin versus IgD, r = 0.489, p = 0.046 and from IgD versus IgG, r = 0.556, p = 0.020. These analyses support a different mechanism of entry of IgD into milk compared to IgG or albumin.(ABSTRACT TRUNCATED AT 250 WORDS)