JohnV. Parry

SENSITIVE ASSAYS FOR VIRAL ANTIBODIES IN SALIVA: AN ALTERNATIVE TO TESTS ON SERUM

Paired serum and saliva specimens were tested by conventional assays and by IgG-capture radioimmunoassays (GACRIA) and enzyme-linked immunosorbent assays (GACELISA) for antibody to hepatitis A virus (HAV, 100 pairs), human immunodeficiency virus (HIV, 53), hepatitis B virus core (HBc, 62), and rubella virus (30). Conventional assays failed to detect viral antibodies in the saliva of 93 of 119 seropositive subjects. However, GACRIA detected the antibodies in both serum and saliva of all subjects seropositive by conventional tests, except 2 saliva specimens false-negative for anti-HBc and 1 false-negative for anti-rubella-virus. For anti-HIV and anti-HBc serum and saliva GACRIA reactivities did not differ significantly, but anti-HAV and anti-rubella-virus GACRIA reactivities were stronger in serum than saliva. GACRIA and GACELISA results on saliva for the four antibodies correlated closely; for anti-HAV and anti-HIV GACELISA and GACRIA were equally accurate. For both saliva and serum, GACRIA was superior to an IgA-capture assay in detecting anti-HAV and anti-HIV.

Determinants of HIV disease progression: six-year longitudinal study in the Edinburgh haemophilia/HIV cohort

Markers of immune function present before infection may determine the subsequent course of disease in HIV-infected individuals. In 1983, we measured immune function in a group of haemophiliacs in Edinburgh. In 1984, 18 of these patients became infected with HIV-1 from contaminated factor VIII. We have followed-up these patients since their seroconversion. The rate of disease progression, as assessed by the appearance or not of AIDS symptoms or signs within five years of seroconversion, was related both to the concentration of total plasma IgM before exposure to infection and to the pattern of specific IgM and IgA anti-HIV response around the time of IgG seroconversion. Disease progression also correlated with concentrations of plasma interleukin-2 receptor (a marker of lymphocyte activation) and with the number and percentage of circulating DR + ve (activated) T cells. Our findings show that the extent of host immune reactivity, which may be genetically determined, is a powerful factor in the pathogenesis of HIV-associated disease.

WHICH ANTI-HTLV III/LAV ASSAYS FOR SCREENING AND CONFIRMATORY TESTING?

In preparation for routine anti-HTLV-III/LAV testing in the UK five commercial assays (A-E) were evaluated using 360 sera selected on clinical and epidemiological grounds. These comprised 220 specimens from blood donors, 83 specimens from patients in high-risk groups, and 57 specimens with features likely to produce false-positive results. Probably erroneous positive results arose from assay A in all three categories and assay B in the second and third categories. These reactions were much more common after specimens had been heated to 56 degrees C for 30 min. Except that an anti-HLA DR4,B5-containing serum was repeatedly positive by C, assays C, D, and E apparently did not give rise to false-positive results. Results by these three assays were also highly reproducible. In tests on serum dilutions the highest titres were obtained by assays A and D, but assays C and E discriminated most clearly between anti-HTLV-III/LAV positive and negative sera. These two assays were rapid and convenient and seemed particularly suitable for testing blood donations. Assay D was almost comparable with them in performance but more difficult to use. The commercial assays C, D and E, an antibody capture assay, and a simple immunofluorescence test could be the basis for a methodologically diverse national system of primary and confirmatory testing for anti-HTLV-III/LAV.

RATIONAL PROGRAMME FOR SCREENING TRAVELLERS FOR ANTIBODIES TO HEPATITIS A VIRUS

A blood test and a saliva test for antibody to hepatitis A virus (anti HAV) were offered to British travellers seeking human normal immunoglobulin (HNIG) prophylaxis. The specimens were tested by an IgG capture and a competitive radioimmunoassay (GACRIA, COMPRIA). By GACRIA 211 subjects were anti-HAV positive and 358 anti-HAV negative on both serum and saliva. 10 other seropositive subjects had weakly positive saliva reactions. There were three discrepant results. For the population investigated HNIG use could be minimised at no extra cost by first testing the saliva of those greater than 40 years old, frequent or long-stay travellers, those born in HAV endemic areas, and those with a history of jaundice. Of the 51% of travellers tested for these reasons 20% were anti-HAV positive. They made up 76% of all those with antibody.

THE INFLUENCE OF DENTAL STATUS ON THE DETECTION OF IgG CLASS ANTI-VIRAL ANTIBODIES IN HUMAN SALIVA

An antibody-capture radioimmunoassay was used to measure levels of IgG class antibodies to rubella and hepatitis A viruses in serum and saliva of 30 edentulous, 30 partially dentate and 31 dentate individuals. The prevalence of seropositivity for rubella was 98.9 per cent and for hepatitis A 73.6 per cent. The serum reactivities were generally greater than those for saliva. There were 8 false-negative results for saliva out of the 182 tests performed, of which 4 were in the edentulous group, 3 in the partially dentate and 1 in the dentate group. For both rubella and hepatitis A virus antibodies the (geometric) mean ratios between the saliva and serum reactivities were similar across the three dental groups. The values for sensitivity, specificity and positive predictive value suggest that assay of saliva for antiviral IgG antibody is a satisfactory technique regardless of dental status.

Variation in the sensitivity of HBsAg screening kits

Summary. Fifteen HBsAg kits from 14 manufacturers were assessed. Their sensitivity was evaluated by testing 150 HBsAg‐positive sera, sera from four donors who were low‐level HBsAg carriers, and sequential specimens from 22 seroconverting individuals together with dilutions of six of these specimens. The British HBsAg Working Standard (0.5IUmL‐1) and the NIBSC/UKBTS HBsAg Monitor Sample (0.125IUmL‐1) were also tested. Five assays failed to detect one of the 150 routine HBsAg‐positive sera. Four assays (Auszyme Monoclonal; Monolisa Ag HBs 2nd generation; Murex HBsAg; Ortho HBsAg Test Systems 3) were able to detect HBsAg in all but one of the six sera from low‐level carriers, whereas one assay (MicroTrak II HBsAg) detected only one of the six. The most sensitive kit (Monolisa Ag HBs 2nd generation) detected HBsAg in 79 specimens from the seroconversion panels; four other kits detected HBsAg in at least 70 specimens, seven in 60–69, two in 50–59 and the least sensitive in 31. Further analysis of the findings on seroconverters indicated a median reduction in the duration of HBsAg detection of 5 days or more for four assays when compared with the most sensitive assay. One kit (Auszyme Monoclonal) detected HBsAg in 15 of the 18 dilutions prepared from the seroconversion specimens, whereas three kits detected HBsAg in fewer than 10 dilutions. Two kits gave negative reactions with the British HBsAg Working Standard on all of five occasions and six were consistently unreactive with the NIBSC/UKBTS HBsAg Monitor Sample; only three kits (Bioelisa, Enzygnost, Murex) were always reactive. There is therefore substantial variation in sensitivity among the HBsAg kits currently available.