SYNOPSIS A gel filtration technique using Sephadex G-200 has been used for the detection of specific IgM in sera from (a) 45 cases of clinical rubella in which diagnostic rises of rubella haemagglutination-inhibiting (HAI) antibody could be demonstrated; (b) 70 cases with clinical evidence of rubella in which a rising titre could not be demonstrated because the first serum sample already had high titre HAI antibodies; and (c) 100 patients in whom rubella was not suspected. The results indicate that the high specificity and sensitivity of the method described make it an appropriate technique for use in the routine diagnosis of acquired rubella.
Eight sera from 125 cases of infectious mononucleosis (IM) were reactive for rubella-specific IgM in an M-antibody capture radioimmunoassay. The reactivity of individual sera varied depending upon the source of the rubella antigen used in the assay. One serum gave strongly positive results with some rubella haemagglutinating antigens but negative results with others and may have contained an IgM antibody which was capable of distinguishing between strains of rubella virus. If the diagnosis of rubella is based solely on detection in solid-phase immunoassay of rubella-specific IgM, IM should be excluded.
Radial haemolysis (RH) was used to test sera for immunity to rubella from 1317 patients attending a general practice. One hundred and forty-one (10.7%) were treated as susceptible and offered an attenuated virus vaccine (RA 27/3). Pre-immunization sera from 43% of these patients were reactive at low levels in RH (less than 15 international units rubella antibody per ml). Pre- (S1) and post- (S2) immunization sera from 66 vaccinees were studied in detail. Antibody was detected by RH, haemagglutination inhibition (HI) and enzyme-linked immunosorbent assay (ELISA), and the specific IgM response was measured by a solid-phase M-antibody capture radioimmunoassay (MACRIA). The vaccine-induced IgM response was only detected if the S1 serum was non-reactive by all tests for rubella antibody. It was weaker than that seen following wild virus infection. It could be detected reliably for six weeks, and in most cases for nine weeks, after immunization. In contrast, patients with S1 specimens reactive by RH, HI or ELISA never showed an IgM response in the S2 specimen despite "significant' antibody rises often being present. It was considered that an IgM response to RA 27/3 was the best indicator of pre-immunization susceptibility to rubella. The failure of many vaccinees to make an IgM response implied that a significant proportion were already immune. It is suggested that the threshold for a report of immunity to rubella could be lowered from 15 i.u. antibody per ml and so fewer women immunized without vaccine being withheld from those who need it.
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