Absence of human T-lymphotrophic virus type I in patients with systemic lupus erythematosus

The role of the human T-cell lymphotropic/leukaemia virus type I (HTLV-I) in the pathogenesis of autoimmune diseases of unknown cause, such as systemic lupus erythematosus (SLE), multiple sclerosis (MS) or Sjögren's syndrome (SS) has been discussed extensively. We have investigated whether SLE is in any way associated with exogenous HTLV-I. Using enzyme immunoassay (EIA), we found no seroreactivity against HTLV-I antigens in any of 24 SLE patients under investigation. Using a radioimmunoprecipitation assay (RIPA), there was also no expression of retroviral tax-protein demonstrable in 24 individuals with SLE. DNA preparations of peripheral blood cells, as well as isolated CD4- and CD8-positive cells, were examined for HTLV-I sequences (pol-, env-, gag-, LTR- and tax-region) using polymerase chain reaction (PCR). We were unable to demonstrate any specific HTLV-I PCR products in SLE specimens. Our data suggest that exogenous HTLV-I is not involved in the pathogenesis of SLE. Systemic lupus erythematosus (SLE) is a multisystem disease of unknown cause characterized by B-cell hyperactivity with hypergammaglobulinaemia and the formation of pathogenic autoantibodies. Patients may also show altered suppressor/helper T-cell ratios. Abnormalities in T-cell function include T-cell lymphopenia, expression of activation antigens and alteration of responses to mitogens and lymphokines. Human retroviruses are known to cause immune aberrations, such as diminished T-cell function and polyclonal B-cell stimulation, which are observed in patients with leukaemias, lymphomas and the acquired immunodeficiency syndrome (AIDS). Human T-cell lymphotropic/leukaemia (HTLV-I) is aetiologically linked with adult virus type I T-cell leukaemia (ATL) and tropical spastic paraparesis. A common feature of the HTLV family is an LTR encoded protein (tax protein, p40tax) which triggers viral protein production in the early stages of a retroviral infection. Detection of p40tax may indicate transcriptional activity of a provirus. Several investigators have examined the possible involvement of HTLV-I in SLE and have produced conflicting results, especially so far as seroreactivity against HTLV-I antigens is concerned. The discovery of HTLV-I like particles in murine lupus might also indicate an important role of exogenous viruses in SLE. Olsen and colleagues describe a high seropositivity to anti-HTLV-I- and anti-HTLV-III antibodies and evidence of viral replication in patients with SLE. Lin et al. also demonstrated anti-HTLV-I antibodies in SLE patients. However, other authors failed to detect anti-HTLV-I antibodies, proviral structures or viral transcripts in SLE. We investigated whether or not there are any indications of the presence of the exogenous retrovirus, HTLV-I, in patients with SLE, at immunological and genetic levels. We found neither immunological nor molecular biological evidence for the existence of HTLV-I in SLE patients. There were some weak suggestions of the presence of possibly endogenous retroviral sequences.