A small particle, named rheumatoid associated parvovirus-like
agent (RA-1 virus), resembles parvoviruses in physicochemical and morphological
properties. It was derived from the synovial tissue of a patient
with severe rheumatoid arthritis. The etiology of rheumatoid arthritis,
a disease thought to be associated with infectious agents ranging from
bacteria to viroids, has evaded investigators for years -- could RA-1 be
involved in causing this debilitating condition? Is RA-1 a true member
of the parvovirus family? Some investigations have been conducted,
but these questions remain unresolved.
Recent studies have identified RA-1 as a DNA parvovirus.
In one study, investigators were able to isolate 24-nm particles in the
brains of mice that had been inoculated with extracts of synovial cells.
A single stranded DNA fragment, approximately 4.5 kilobases in size, was
extracted from the particles. The apparent small size of the isolate,
the particles' resistance, and the particle pathogenesis in neonatal rodents
also suggests that it is a parvovirus. However, studies of the molecular
properties of this DNA species with restriction enzymes show that it has
a cleavage pattern that differs from existing parvoviruses. It has not
been established that RA-1 is related to existing parvoviruses of mammalian
species.
In a study conducted with neonatal mice, the RA-1 virus
elicited a syndrome in the animals that included neurological disturbances,
alopecia (sporadic loss of body hair), blepharitis, dwarfism, "masking,"
permanent crippling of the limbs and a rigid curvature of the thoracic
spine.
The RA-1 virus remains an attractive candidate for the
induction of rheumatoid arthritis in humans, as well as a candidate for
membership in the parvovirus family. Polyclonal antibodies detect
the presence of RA-1 in patients with rheumatoid arthritis, but not in
persons with osteoarthrits, which also supports the possible link between
RA-1 and chronic rheumatoid arthritis in humans. The exact nature
of RA-1, its relationship to existing parvoviruses, and its role in causing
rheumatoid arthritis are all questions that remain to be resolved in future
studies.