HDL associates with insulin resistance and beta-cell dysfunction in South Asian families at risk of type 2 diabetes.

OBJECTIVE: Dyslipidemia precedes type 2 diabetes (T2D) and worsens with increasing glucose intolerance. First degree relatives of T2D patients have an increased risk to develop dyslipidemia and glucose intolerance. The aim of the present study was to assess the relation between the development of dyslipidemia and glucose intolerance in first-degree relatives of T2D patients. RESEARCH DESIGN AND METHODS: Fasting lipoprotein profiles were determined by density gradient ultracentrifugation in T2D patients and their first-degree relatives (42 Caucasians and 33 South Asians), and in 29 normoglycemic controls from non-T2D families. Glucose tolerance, insulin sensitivity index (ISI) and insulin disposition index (DI) were assessed by an extended, frequently sampled oral glucose tolerance test (OGTT), and fractional insulin synthesis rate (FSR) was measured by 13C-leucine enrichment in urinary C-peptide during the OGTT. RESULTS: Of the first-degree relatives, 40, 16 and 19 had NGT, prediabetes and T2D, respectively. NGT family members had lower plasma HDL-cholesterol (HDLC) (1.34 ± 0.07 vs 1.58 ± 0.06 mmol/L; p = 0.015), HDL2-C (0.41 ± 0.05 vs 0.57 ± 0.05 mmol/L; p = 0.021) and HDL3-C (0.62 ± 0.03 vs 0.72 ± 0.02 mmol/L; p = 0.043) than controls. HDL2-C levels tended to decrease with increasing glucose intolerance state. In South Asians, buoyant LDL-C levels decreased with increasing glucose intolerance state (p = 0.006). In South Asian families, HDL-C correlated with both ISI and DI (ß 0.42; p = 0.04 and ß 0.53; p = 0.01, respectively), whereas HDL2-C and HDL3-C levels correlated with DI (ß 0.64; p = 0.002 and ß 0.57; p = 0.005, respectively). HDL2-C and plasma triglyceride correlated with FSR (ß 0.48; p = 0.033 and ß -0.50; p = 0.029, respectively). CONCLUSIONS: Low HDL2-C and HDL3-C levels are present in NGT first-degree relatives of T2D patients, and HDL2-C tend to decrease further with increasing glucose intolerance. In South Asian families HDL2-C and HDL3-C levels linked predominantly to deteriorating beta cell function.

Signals that initiate somatic hypermutation of B cells in vitro.

Somatic hypermutation is initiated as B lymphocytes proliferate in germinal centers. The signals that switch on the mutation process are unknown. We have derived an in vitro system to define signals that will initiate mutation in normal, naive splenic B cells. We find that three signals are required to allow detection of somatic mutation in vitro; these are anti-Ig, anti-CD40, and anti-CD38. If any one of these is omitted, mutation remains off. We show that CD40 is obligatory in vivo, as CD40 knockout mice exhibit no Ag-driven mutation. In contrast, CD38 is not, as CD38 knockout mice mutate normally. We believe that, in vitro, CD38, in combination with other stimuli, drives extensive cell division, allowing the detection of mutated sequences. However, in germinal centers in vivo, proliferative activity is instigated by a different molecule. This is the first demonstration of the initiation of hypermutation in vitro with normal splenic B cells using defined stimuli.

Somatic mutation of immunoglobulin V genes in vitro.

The molecular mechanism behind affinity maturation is the introduction of point mutations in immunoglobulin (Ig) V genes, followed by the selective proliferation of B cells expressing mutants with increased affinity for antigen. An in vitro culture system was developed in which somatic hypermutation of Ig V genes was sustained in primed B cells. Cognate T cell help and cross-linking of the surface Ig were required, whereas the addition of lipopolysaccharide or a CD40 ligand to drive proliferation was insufficient. This system should facilitate understanding of the molecular and cellular mechanisms that regulate somatic mutation and B cell selection.

Memory B cell development but not germinal center formation is impaired by in vivo blockade of CD40-CD40 ligand interaction.

To study the role of the CD40-CD40 ligand interaction in the development of memory B cells and its level of action during primary antibody responses in vivo, mice were injected with a soluble CD40 fusion protein (sCD40-gamma 1), so as to block the interaction. The effects of the treatment on the primary antibody response were reminiscent of hyper-immunoglobulin M (IgM) syndrome (HIMG1): antigen-specific IgG responses were grossly inhibited whereas the IgM response was augmented severalfold. The latter observation suggests that there is a T-dependent, CD40 ligand-independent pathway of B cell activation that leads to IgM responses and that a significant component of the IgM in HIMG1 patients is derived from T-dependent responses. The secondary response was not readily blocked by sCD40-gamma 1 treatment, indicating a relative independence of CD40 ligation of antigen-experienced B cells. The most striking finding from these studies is that the development of memory B cell populations (measured by adoptive transfer) is grossly impaired by administration of sCD40-gamma 1 during the early induction phase of the response. It is surprising that although the generation memory is diminished, there is no quantitative difference in the development of germinal centers. Whereas entry of B cells into the memory cell pathway is dependent on CD40 ligation, the clonal expansion of the potential memory precursors in germinal centers seems not to require a CD40 signal.

Phenotypic and molecular characterization of human monoclonal TCR gamma/delta T-cell lines from jejunum and colon of healthy individuals.

We have performed a phenotypic and molecular analysis of monoclonal TCR gamma/delta T-cell lines derived from jejunal and colonic biopsies of healthy individuals. Flow cytometric analysis employing a panel of 24 monoclonal antibodies (MoAbs) demonstrated that intestinal TCR gamma/delta intraepithelial lymphocytes (IEL) constitute a phenotypically heterogeneous population. Nucleotide sequence analysis of expressed TCR delta variable (V) regions revealed the dominant utilization of the V delta 2 and D delta 3 gene segments and frequent rearrangement of J delta 3. IEL V delta regions displayed extensive junctional diversity as a result of N and P insertion and the utilization of D delta 3 in all three reading frames. The results demonstrate that intestinal TCR gamma/delta T cells from healthy individuals constitute a phenotypically heterogeneous population expressing V delta regions that differ from their systemic counterparts.

Selective enhancement of Leu-CAM expression by interleukin 6 during differentiation of human promonocytic U937 cells.

Interleukin 6 (IL-6) is a cytokine with multiple biological activities on various tissues and cells. We have investigated the effect of recombinant human IL-6 (rhIL-6) on growth and differentiation of U937. Recombinant human IL-6 induced a dose-dependent growth inhibition, apparent around day 4, of up to 50% by day 8 of culture. Concomitant with this, changes in cytochemical activities were observed, indicative of differentiation. A panel of U937 antigens was analysed after culture with rhIL-6. Expression of the majority of these membrane antigens was unaffected, with the exception of two classes. First, rhIL-6 had a profound effect on members of the leucocytic cell adhesion molecules (Leu-CAM) family. Expression of the alpha-chain of CR3 (complement receptor 3; CD11b) was enhanced in a dose-dependent fashion, with maximal expression around day 7. Parallel to this a simultaneous increase in beta-chain (CD18) expression was found. Furthermore, enhanced expression of CR3 was, accompanied by increased rosetting with sheep erythrocytes sensitized with C3bi. A much lower, but significant, enhancement was observed for the alpha-chain of the p150,95 antigen (CD11c). Expression of leucocyte function-associated antigen-1, (LFA-1), (CD11a/CD18) remained unchanged. Remarkably, however, expression of a ligand of LFA-1, intercellular adhesion molecule-1 (ICAM-1; CD54), was enhanced with similar kinetics as CR3 and p150,95. A specific anti-rhIL-6 antiserum completely inhibited the IL-6 effect. These observations provide further support for an important role of IL-6 in the regulation of myeloid cell development in man.