Samia Akhtar

A single-nucleotide polymorphism in the gene encoding lymphoid protein tyrosine phosphatase ( PTPN22 ) confers susceptibility to generalised vitiligo

Vitiligo is an acquired hypomelanotic skin disorder resulting from the loss of functional melanocytes from the cutaneous epidermis and autoimmunity has been suggested to play a part in its pathogenesis. Recently, the missense R620W polymorphism in the PTPN22 gene, which encodes lymphoid protein tyrosine phosphatase (LYP), has been associated with susceptibility to autoimmune disorders. The objective of this study was to ascertain if the disease-associated 1858T allele was also associated with generalised (nonsegmental) vitiligo and so the frequencies of the PTPN22 1858C/T alleles were investigated in 165 English patients with generalised vitiligo and 304 ethnically matched control subjects. The results indicated that the 1858T allele was significantly over-represented in the vitiligo patient group compared with the control cohort. Of 330 vitiligo alleles, 48 (14.5%) encoded the Trp620 variant compared to 52 of 608 (8.6%) control alleles (P=0.006; odds ratio=1.82, 95% confidence interval=1.17–2.82). The results indicate that the LYP missense R620W polymorphism may have an influence on the development of generalised vitiligo and provide further evidence for autoimmunity as an aetiological factor with respect to this disease.

Primary and Booster Salivary Antibody Responses to a 7-Valent Pneumococcal Conjugate Vaccine in Infants

Salivary anticapsular antibody responses to a 7-valent pneumococcal conjugate vaccine (7VPnC) were measured in healthy infants. Infants received diphtheria-tetanus-pertussis/Haemophilus influenzae type b (DTP/Hib; group 1), DTP/Hib and 7VPnC (group 2), or DTP and 7VPnC/Hib (group 3) at ages 2, 3 and 4 months. All children received 23-valent pneumococcal polysaccharide vaccine at age 13 months. Salivary IgA and IgG responses to primary immunizations were generally poor. IgA mean concentrations at age 5 months were higher in the treatment groups than in control subjects for serotype 14 only (P<.001). At age 13-14 months, there were marked increases in IgA (mean fold difference, 3.7-4.9) and IgG (mean fold difference, 4. 1-11.7) levels for serotypes 4, 9V, 14, and 19F and serotypes 4, 18C, 19F, and 23F, respectively, in the treatment groups. This contrasts with low IgA (1.2 and 1.4) and IgG (1.3 and 2.2) mean fold differences for non-7VPnC serotypes 1 and 5. The results suggest that 7VPnC primes for mucosal memory responses in infants.

Primary and Booster Mucosal Immune Responses to Meningococcal Group A and C Conjugate and Polysaccharide Vaccines Administered to University Students in the United Kingdom

ABSTRACT Meningococcal group A+C capsular polysaccharide (PS) conjugate vaccines may prime for serum immunoglobulin G (IgG) memory responses to meningococcal capsular PS. It is not known whether these vaccines induce immunological memory at the mucosal level, which may be important in reducing nasopharyngeal carriage. Mucosal immune responses to meningococcal conjugate and PS vaccines in young adults were investigated. Healthy university students were randomized to receive either a groups A+C meningococcal conjugate vaccine (MACconj,n = 100) or a group A+C meningococcal PS vaccine (MACPS, n = 95). One year after the primary immunization, both groups were randomized again to receive a MACconj or a MACPS booster vaccination. Saliva samples were collected before and 1 month after the primary and booster vaccinations. Anti-meningococcal A (MenA) and C (MenC) PS IgA and IgG antibody levels were measured by a standard enzyme-linked immunosorbent assay. After the primary vaccination, salivary MenA and MenC IgG and MenA IgA concentrations were significantly increased after immunization with both MACconj and MACPS vaccines, but the salivary Men C IgA level was increased only after MACPS vaccine (P < 0.01). IgA responses to both serogroups were greater for MACPS than MACconj vaccine (P < 0.05), whereas no significant differences were seen for IgG responses. MenA IgG titers were higher after the MACPS booster in MACconj-primed subjects than after the MACPS primary vaccination, suggesting the presence of IgG memory. Antibody responses to a dose of either MACPS or MACconj were not significantly reduced in those previously given MACPS compared to the primary responses to those vaccines. Meningococcal A+C conjugate and PS vaccines induce significant mucosal responses in young adults. MACconj priming may induce IgG memory at the mucosal level, which is likely to be a reflection of an anamnestic serum IgG response. No evidence of mucosal hyporesponsiveness was observed after MACPS priming in this study.

Autoantibodies against tyrosine hydroxylase in patients with non-segmental (generalised) vitiligo.

Abstract:  Vitiligo is an acquired idiopathic hypomelanotic skin disorder characterised by depigmented macules because of loss of cutaneous melanocytes. Although the exact cause of vitiligo remains obscure, evidence suggests that autoimmunity plays a role in the pathogenesis of the disease. Previously, tyrosine hydroxylase (TH) was identified as a putative autoantigen in vitiligo using phage‐display technology. In this study, the prevalence of TH antibodies in patients with vitiligo was investigated. A radioimmunoassay (RIA) was used to detect TH antibodies in sera from patients with either non‐segmental vitiligo (n = 79), segmental vitiligo (n = 8) or other autoimmune diseases without concomitant vitiligo (n = 91). Sera from healthy individuals (n = 28) were also tested. Patients with segmental vitiligo, healthy controls and patients with other autoimmune diseases without concomitant vitiligo were all negative for TH antibody reactivity. Of 79 patients with non‐segmental vitiligo, 18 (23%) were positive for TH antibodies in the RIA, and a significant increase in the prevalence of TH antibodies in patients with non‐segmental vitiligo was evident when compared with controls (P = 0.003). TH antibody prevalence was also significantly elevated in patients with active vitiligo compared to those with stable disease (P = 0.009). Overall, the results indicate that TH is an antibody target in non‐segmental but not in segmental vitiligo and that TH antibodies appear to be more frequent in patients with active vitiligo.

Testosterone suppresses the expression of regulatory enzymes of fatty acid synthesis and protects against hepatic steatosis in cholesterol-fed androgen deficient mice

AIMS Non-alcoholic fatty liver disease and its precursor hepatic steatosis is common in obesity and type-2 diabetes and is associated with cardiovascular disease (CVD). Men with type-2 diabetes and/or CVD have a high prevalence of testosterone deficiency. Testosterone replacement improves key cardiovascular risk factors. The effects of testosterone on hepatic steatosis are not fully understood. MAIN METHODS Testicular feminised (Tfm) mice, which have a non-functional androgen receptor (AR) and very low serum testosterone levels, were used to investigate testosterone effects on high-cholesterol diet-induced hepatic steatosis. KEY FINDINGS Hepatic lipid deposition was increased in Tfm mice and orchidectomised wild-type littermates versus intact wild-type littermate controls with normal androgen physiology. Lipid deposition was reduced in Tfm mice receiving testosterone treatment compared to placebo. Oestrogen receptor blockade significantly, but only partially, reduced the beneficial effects of testosterone treatment on hepatic lipid accumulation. Expression of key regulatory enzymes of fatty acid synthesis, acetyl-CoA carboxylase alpha (ACACA) and fatty acid synthase (FASN) were elevated in placebo-treated Tfm mice versus placebo-treated littermates and Tfm mice receiving testosterone treatment. Tfm mice on normal diet had increased lipid accumulation compared to littermates but significantly less than cholesterol-fed Tfm mice and demonstrated increased gene expression of hormone sensitive lipase, stearyl-CoA desaturase-1 and peroxisome proliferator-activated receptor-gamma but FASN and ACACA were not altered. SIGNIFICANCE An action of testosterone on hepatic lipid deposition which is independent of the classic AR is implicated. Testosterone may act in part via an effect on the key regulatory lipogenic enzymes to protect against hepatic steatosis.

Function-blocking autoantibodies to the melanin-concentrating hormone receptor in vitiligo patients.

Vitiligo is a common depigmenting skin disorder resulting from the loss of melanocytes in the cutaneous epidermis. Although the cause of the disease remains obscure, autoimmune mechanisms are thought to be involved. Recently, melanin-concentrating hormone receptor (MCHR)-binding autoantibodies have been identified in vitiligo patients. In the present study, we aimed to determine if MCHR autoantibodies could also affect receptor function either by direct activation or by blocking its response to melanin-concentrating hormone. The results indicated that 10/18 (56%) vitiligo patient IgG samples inhibited the function of MCHR expressed in a Chinese hamster ovary cell line. In contrast, neither control (n=20) nor SLE patient (n=10) IgG samples blocked receptor function. Compared with healthy controls, MCHR function-blocking autoantibodies were found at a significantly increased frequency in the vitiligo patient group (P=0.0004). No MCHR-activating autoantibodies were detected in any of the vitiligo patient, SLE patient or control IgG samples that were analysed. In addition, vitiligo patient IgGs were tested for MCHR autoantibodies that could mediate antibody-dependent cell-mediated cytotoxicity via the receptor. However, this could only be demonstrated in two vitiligo patient sera. Overall, this work has provided additional evidence that MCHR is a B-cell autoantigen in vitiligo and has demonstrated the existence of MCHR function-blocking autoantibodies further to the receptor-binding autoantibodies previously reported.

Mapping of human autoantibody binding sites on the calcium-sensing receptor.

Previously, we have demonstrated the presence of anti‐calcium‐sensing receptor (CaSR) antibodies in patients with autoimmune polyglandular syndrome type 1 (APS1), a disease that is characterized in part by hypoparathyroidism involving hypocalcemia, hyperphosphatemia, and low serum levels of parathyroid hormone. The aim of this study was to define the binding domains on the CaSR of anti‐CaSR antibodies found in APS1 patients and in one patient suspected of having autoimmune hypocalciuric hypercalcemia (AHH). A phage‐display library of CaSR peptides was constructed and used in biopanning experiments with patient sera. Selectively enriched IgG‐binding peptides were identified by DNA sequencing, and subsequently, immunoreactivity to these peptides was confirmed in ELISA. Anti‐CaSR antibody binding sites were mapped to amino acid residues 41–69, 114–126, and 171–195 at the N‐terminal of the extracellular domain of the receptor. The major autoepitope was localized in the 41–69 amino acid sequence of the CaSR with antibody reactivity demonstrated in 12 of 12 (100%) APS1 patients with anti‐CaSR antibodies and in 1 AHH patient with anti‐CaSR antibodies. Minor epitopes were located in the 114–126 and 171–195 amino acid domains, with antibody reactivity shown in 5 of 12 (42%) and 4 of 12 (33%) APS1 patients, respectively. The results indicate that epitopes for anti‐CaSR antibodies in the AHH patient and in the APS1 patients who were studied are localized in the N‐terminal of the extracellular domain of the receptor. The present work has demonstrated the successful use of phage‐display technology in the discovery of CaSR‐specific epitopes targeted by human anti‐CaSR antibodies.

An insertion/deletion polymorphism in the gene encoding angiotensin converting enzyme is not associated with generalised vitiligo in an English population.

Vitiligo is an acquired hypomelanotic skin disorder characterised by circumscribed depigmented macules resulting from the loss of functional melanocytes from the cutaneous epidermis and autoimmunity has been suggested to play a role in the pathogenesis of the disease. Recently, an insertion/deletion (I/D) polymorphism of a 287-base pair repetitive sequence in intron 16 of the angiotensin converting enzyme (ACE) gene has been associated with autoimmune disease and with the development of vitiligo. In this study, the distribution of ACE gene I/D genotypes was investigated in a population of 106 English patients with generalised (non-segmental) vitiligo and 174 ethnically matched healthy controls using a restriction fragment length polymorphism-polymerase chain reaction genotyping method. No significant difference in the frequencies of II, ID and DD genotypes was detected between vitiligo patients and control subjects (P=0.35). The same result was evident for the genotype distribution in vitiligo patients with an autoimmune disease and for those without when compared with controls (P=0.33 and P=0.53, respectively). In addition, the results indicated that the D allele was not significantly over-represented in the group of patients with vitiligo compared with controls (P=0.42) and that this was also the case for patients with and without associated autoimmunity (P=0.40 and P=0.62, respectively).

The role of androgen receptor CAG repeat polymorphism and other factors which affect the clinical response to testosterone replacement in metabolic syndrome and type 2 diabetes: TIMES2 sub-study

CONTEXT The TIMES2 (testosterone replacement in hypogonadal men with either metabolic syndrome or type 2 diabetes) study reported beneficial effects of testosterone replacement therapy (TRT) on insulin resistance and other variables in men with diabetes or metabolic syndrome. The androgen receptor CAG repeat polymorphism (AR CAG) is known to affect stimulated AR activity and has been linked to various clinically relevant variables. OBJECTIVE To assess the role of AR CAG in the alteration of clinical response to TRT in the TIMES2 study. DESIGN Subgroup analysis from a multicentre, randomised, double-blind, placebo-controlled and parallel group study. SETTING Outpatient study recruiting from secondary and primary care. PATIENTS A total of 139 men with hypogonadism and type 2 diabetes or metabolic syndrome, of which 73 received testosterone during the TIMES2 study. INTERVENTION Testosterone 2% transdermal gel vs placebo. MAIN OUTCOME MEASURE Regression coefficient of AR CAG from linear regression models for each variable. RESULTS AR CAG was independently positively associated with change in fasting insulin, triglycerides and diastolic blood pressure during TRT with a trend to association with HOMA-IR - the primary outcome variable. There was a trend to negative association between AR CAG and change in PSA. There was no association of AR CAG with change in other glycaemic variables, other lipid variables or obesity. CONCLUSION AR CAG affected the response of some variables to TRT in the TIMES2 study, although the association with HOMA-IR did not reach significance. Various factors may have limited the power of our study to detect the significant associations between AR CAG, testosterone levels and change in variables with testosterone treatment. Analysis of similar data sets from other clinical trials is warranted.