Nucleotide sequence analysis of human T-cell lymphotropic virus type I pX and LTR regions from patients with sicca syndrome

HTLV-1 infection: what determines the risk of inflammatory disease?

Human T-lymphotropic virus type 1 (HTLV-1) is an exogenous retrovirus that persists lifelong in the infected host. Infection has been linked to a spectrum of diverse diseases: adult T cell leukemia, encephalomyelopathy, and predisposition to opportunistic bacterial and helminth infections. Applications of new technologies and biological concepts to the field have provided new insights into viral persistence and pathogenesis in HTLV-1 infection. Here, we summarize the emerging concepts of dynamic HTLV-1-host interactions and propose that chronic interferon (IFN) production causes tissue damage in HTLV-1-associated inflammatory diseases.

Hijacking the T-cell communication network by the human T-cell leukemia/lymphoma virus type 1 (HTLV-1) p12 and p8 proteins

The non-structural proteins encoded by the orf-I, II, III, and IV genes of the human T-cell leukemia/lymphoma virus type 1 (HTLV-1) genome, are critical for the modulation of cellular gene expression and T-cell proliferation, the escape from cytotoxic T-cells and natural killer cells, and virus expression. In here, we review the main functions of the HTLV-1 orf-I products. The 12kDa product from orf-I (p12) is proteolytically cleaved within the endoplasmic reticulum (ER) to generate the 8kDa protein (p8). At the steady state, both proteins are expressed at similar levels in transfected T-cells. The p12 protein remains in the ER and cis-Golgi, whereas the p8 protein traffics to the cell surface and is recruited to the immunological synapse. The p12 and the p8 proteins have seemingly opposite effects on T-cells; the ER resident p12, modulates T-cell activation and proliferation, whereas p8 induces T-cell anergy. The p8 protein also increases the formation of cellular conduits, is transferred to neighboring T-cells, and increases virus transmission. The requirement for HTLV-1 infectivity of orf-I is demonstrated by the loss of virus infectivity in macaques exposed to an engineered virus, whereby expression of orf-I was ablated. Altogether the current knowledge demonstrates that the concerted activity of p8 and p12 is essential for the persistence of virus infected cells in the host.

Genetic markers on the HTLV-1 p12I protein sequences from Brazilian HAM/TSP patients and asymptomatic HTLV-1 carrier isolates

The human T cell leukemia/lymphotropic virus type-1 (HTLV-1) genome has approximately 9 kb and contains the pX region that codes for regulatory and accessory proteins. The pX ORF-I encodes for the p12 protein, a 99 aa peptide, which presents several functional putative domains, such as leucine zipper motifs, SH3- binding motifs, and a dileucine motif, p12I. Also, a rare p12IK88 allele was found mainly in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients, suggesting it is a marker of pathogenesis, although recent studies showed p12IK in asymptomatic HTLV-1 carriers. To extend the observations on p12I motifs, we sequenced 26 p12I from HAM/TSP patients and asymptomatic HTLV-1 carriers. Amino acid analysis of 48 p12I motifs demonstrated the presence of several alleles, but the allelic variation, including p12IK, was not prevalent in HAM/TSP isolates. Nonetheless, some genetic markers were recognized in association with isolates from HTLV-1a subgroup B and Brazilian HTLV-1aA strains.

Sjogren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease affecting the exocrine glands, primarily the salivary and lacrimal glands. It has been suggested that exogenous agents may trigger SS in genetically predisposed individuals. However, at present, the etiology of SS is far from being understood, and no direct evidence for any of these triggers has been presented. The salivary and lacrimal glands from patients with SS harbor unique and highly selected T- and B-cell populations. Disturbance in glandular cell apoptosis may be one possible explanation for the sicca symptoms in SS. However, discrepancies between glandular destruction and salivary flow give rise to processes causing glandular dysfunction preceding or triggering glandular cell destruction. Recent reports suggested autoantibodies inhibiting neuronal innervation of acinar cells and defective water transport to be implicated in salivary secretion deficiency observed in SS. Several types of autoantibodies have been suggested to contribute to the pathogenesis of SS. However, how the tolerance to these structures is broken down is unknown at present. Studies on B-cell activating factor indicated that diminished apoptosis and disturbed B-cell maturation could be responsible for the occurrence of autoreactive B-cells and B-cell hyperreactivity. B-cell activation may also provide a basis for lymphoma development observed in up to 5% of the patients with SS.

Role of viruses in systemic lupus erythematosus and Sjögren syndrome

Systemic lupus erythematosus and Sjögren syndrome remain elusive in the description of their underlying etiologic causes and pathogenic mechanisms. Although underlying genetic predisposition appears to contribute to both diseases based on twin and other genetic studies, additional factors must play a role. Over the decades additional factors, such as hormonal influence, UV light, environmental exposures (e.g., silica, solvents), and infectious agents have been postulated to play a role. Over the past few years additional information has been published concerning roles of various infectious agents in both lupus and Sjögren syndrome. Although the understanding of this field is still incomplete, significant advances are being made.