No abstract

Unprotected receptive anal intercourse is a well-recognized risk factor for infection with human immunodeficiency virus-type 1 (HIV-1). Isolated human case reports have implicated HIV-1 transmission by oral-genital exposure. Adult macaques exposed nontraumatically to cell-free simian immunodeficiency virus (SIV) through the oral route became infected and developed acquired immunodeficiency syndrome (AIDS). The minimal virus dose needed to achieve systemic infection after oral exposure was 6000 times lower than the minimal dose required to achieve systemic infection after rectal exposure. Thus, unprotected receptive oral intercourse, even in the absence of mucosal lesions, should be added to the list of risk behaviors for HIV-1 transmission.

A novel diagnostic immunoassay testing procedure for hepatitis B virus core antibody (anti-HBc) using homogeneous purified full-length hepatitis B virus core antigen (HBcAg) capsids obtained from Escherichia coli was compared with Abbott Architect anti-HBc chemiluminescent microparticle immunoassay (CMIA; indirect method) against a library of specimens. A monoclonal anti-HBc neutralization confirmatory assay was then used to determine the degree of discordance between specimens. The new assay was found to be superior in both sensitivity and specificity.Antibodies (anti-HBc) to hepatitis B virus (HBV) core antigen (HBcAg) are present in current and past HBV infections. Anti-HBc antibodies represent a long-term serological marker of HBV infection, initially appearing during the acute phase of the infection and generally persisting thereafter (16). Thus, as anti-HBc is a universal marker of HBV infection, routine blood donor screening for anti-HBc has been implemented in some countries with low endemicity. It is a cost-effective method of screening. Such screening procedures have resulted in a decrease in the risk of posttransfusion HBV infections (12). In some individuals, the only serological marker of HBV infection is the presence of anti-HBc antibodies (10, 24), and thus detection of "anti-HBcAg alone" could reflect unrecognized "occult" HBV infection and physicians should consider investigating such patients with HBV molecular tests (21). Additionally, isolated anti-HBc can be used as a marker to assess the risk of HBV reactivation in patients undergoing therapy that could result in immunosuppression or patients who are HIV positive (17) or hepatitis C virus (HCV) positive (25).With these uses in mind, having a more efficient and reliable assay for anti-HBc is desirable. Most current commercially available anti-HBc assays have poor sensitivity or specificity (2, 19) and can be attributed to the inferior performance of the competitive immunoassay, especially for detecting low-titer antiHBc-reactive samples. False-positive reactivity can partially be attributed to unspecific activation of premature B lymphocytes causing the production of IgM, IgA, or IgM-related molecules without previous exposure to HBV (18,19). The specificity of competitive assays for anti-HBc can be significantly improved by addition of mild reducing agents, but such modified procedures often lead to the loss of sensitivity, particularly for IgM anti-HBc (23). In this study, a novel immunoassay for anti-HBc based on the double-antigen sandwich enzyme-linked immunosorbent assay (ELISA) method is compared with a commercial anti-HBc assay, the Architect chemiluminescent microparticle immunoassay (CMIA). MATERIALS AND METHODSExpression and purification of full-length rHBcAg in E. coli. Two full-length HBcAg genes were obtained by chemosynthesis: AB090269 (genotype D, named CpD) and AB014368 (genotype C, named CpC). The rare arginine codes in Escherichia coli (AGA and AGG) located in the HBcAg gene were changed to CGT. The two fragments were inse...