Increased frequency of the CTLA-4 49 A/G polymorphism in patients with acquired haemophilia A compared to healthy controls.

Acquired haemophilia (AH) is an autoimmune disorder characterized by autoantibodies against endogenous factor VIII (FVIII). Half of the patients present with an underlying disease known to cause the FVIII autoantibodies whereas in the other half the disease is of idiopathic nature. Recently, it has been shown that variants of the polymorphic cytotoxic T lymphocyte antigen-4 (CTLA-4) gene are associated with autoimmune diseases and also represent a risk factor for inhibitor formation in inherited haemophilia A. In the present study, we investigated whether CTLA-4 variants also play a role in the pathogenesis of AH. Therefore, we analyzed three single nucleotide polymorphisms (SNPs) of the CTLA-4 gene (-318 C/T, +49 A/G and CT60 A/G) in 57 AH patients and 98 controls. The CTLA-4 + 49 G allele occurred with a significantly higher frequency in patients with AH compared with controls [odds ratio (OR) = 2.17, 95% confidence interval (CI): 1.36-3.48, P = 0.001]. This effect was mainly caused by a higher frequency of the 49 G allele in female patients (OR = 5.1, 95% CI: 1.76-15.02, P = 0.002), whereas in males the frequencies were not significantly different (OR = 1.4, P = 0.5). A higher frequency of the G allele was also observed in the subcohort with AH and underlying autoimmune disease (OR = 3.1, P = 0.04). Our observations of a higher frequency of the CTLA-4 + 49 A/G SNP in AH patients are in concordance with findings in other autoimmune disorders. In conclusion, on the background of the CTLA-4 gene polymorphism, further genetic and/or environmental factors might contribute to and finally trigger the clinical manifestation of AH.

Immunomodulation by filarial nematodes.

In order to chronically infect their hosts, filarial nematodes have generated a range of strategies to evade and down-modulate the host's immune system. The recent concept of suppression of immune responses by regulatory T cells has in part benefited from examinations in human and murine filariasis. Its further development in basic immunology animal models has in turn helped to better understand down-regulatory immune mechanisms in filariasis. Thus, filarial nematodes orchestrate down-regulation by inducing regulatory T cells and alternatively activated macrophages, which are able to suppress both Th1 and Th2 responses. Regulatory T cells can also induce the secretion of IgG4 from B cells as another arm of modulation. Dendritic cells are down-regulated upon first encounter with infective L3 larvae. Failure to respond to down-regulatory induction is based on genetic traits in hosts and leads to reduced parasite loads, albeit at the expense of pathology and disease. Since down-regulation in chronically and heavily infected hosts extends to third-party antigens, it is essential to analyse the impact of filarial infection for vaccination, allergy and important coinfections such as malaria, in order to foresee and avert potentially disastrous consequences of filariasis control programmes.

Antigen-specific cellular hyporesponsiveness in a chronic human helminth infection is mediated by T(h)3/T(r)1-type cytokines IL-10 and transforming growth factor-beta but not by a T(h)1 to T(h)2 shift.

Exposure to infective larvae of the filarial nematode Onchocerca volvulus (Ov) either results in patent infection (microfilaridermia) or it leads to a status called putative immunity, characterized by resistance to infection. Similar to other chronic helminth infections, there is a T cell proliferative hyporesponsiveness to Ov antigen (OvAg) by peripheral blood mononuclear cells (PBMC) from individuals with patent infection, i.e. generalized onchocerciasis (GEO), compared to PBMC from putatively immune (PI) individuals. In this study, mechanisms mediating this cellular hyporesponsiveness in GEO were investigated: the low proliferative response in PBMC from GEO individuals was associated with a lack of IL-4 production and significantly lower production of IL-5 compared to those from PI individuals, arguing against a general shift towards a T(h)2 response being the cause of hyporesponsiveness. In contrast, IL-10 and transforming growth factor (TGF)-beta, two cytokines associated with a T(h)3 response, seemed to mediate hyporesponsiveness: PBMC from individuals with GEO produced significantly more IL-10, and T cell proliferative hyporesponsiveness in this group could be reversed by the addition of anti-IL-10 and anti-TGF-beta antibodies. Hyporesponsiveness was specific for OvAg and not observed upon stimulation with related nematode antigens, arguing for a T cell-mediated, Ov-specific down-regulation. Ov-specific T cells could be cloned from GEO PBMC which have a unique cytokine profile (no IL-2 but high IL-10 and/or TGF-beta production), similar to the T cell subsets known to suppress ongoing inflammation (T(h)3 and T(r)1), indicating that this cell type which has not been found so far in infectious diseases may be involved in maintaining Ov-specific hyporesponsiveness.

Characterization of human CD4(+) T-cell clones recognizing conserved and variable epitopes of the Lassa virus nucleoprotein.

T cells must play the major role in controlling acute human Lassa virus infection, because patients recover from acute Lassa fever in the absence of a measurable neutralizing antibody response. T cells alone seem to protect animals from a lethal Lassa virus challenge, because after experimental vaccination no neutralizing antibodies are detectable. In order to study human T-cell reactivity to single Lassa virus proteins, the nucleoprotein (NP) of Lassa virus, strain Josiah, was cloned, expressed in Escherichia coli, and affinity purified. Peripheral blood mononuclear cells (PBMC) obtained from 8 of 13 healthy, Lassa virus antibody-positive individuals living in the Republic of Guinea, western Africa, were found to proliferate in response to the recombinant protein (proliferation index >/=10). PBMC obtained from one individual with a particularly high proliferative response were used to generate 50 NP-specific T-cell clones (TCC). For six of these the epitopes were mapped with overlapping synthetic peptides derived from the sequence of the NP. These CD4(+) TCC displayed high specific proliferation and produced mainly gamma interferon upon stimulation with NP. Because variation of up to 15% in the amino acid sequences of the structural proteins of naturally occurring Lassa virus variants has been observed, the reactivity of the TCC with peptides derived from the homologous epitopes of the Nigeria strain of Lassa virus and of the eastern Africa arenavirus Mopeia was tested. With the Nigeria strain of Lassa virus the levels of homology were 100% for two of these epitopes and 85% for three of them, whereas homology with the respective Mopeia epitopes ranged from 92 to 69%. Reactivity of the TCC with peptides derived from the variable epitopes of the Nigeria strain and of Mopeia was reduced or completely abolished. This report shows for the first time that seropositive individuals from areas of endemicity have very strong memory CD4(+) T-cell responses against the NP of Lassa virus, which are partly strain specific and partly cross-reactive with other Lassa virus strains. Our findings may have important implications for the strategy of designing recombinant vaccines against this mainly T-cell-controlled human arenavirus infection.