An
enzyme-linked
immunosorbent assay (ELISA) for detection of
immunoglobulin G (
IgG) and
IgM to
cardiolipin,
lecithin, and
cholesterol (VDRL [
Venereal Disease Research Laboratory] ELISA) is described. The specificity of the VDRL ELISA for
IgG and
IgM was 99.6 and 99.5%, respectively, with sera from 1,008 persons without
syphilis. For a group of patients with false-positive results in traditional nontreponemal tests and for patients with
autoimmune diseases, the VDRL ELISA for
IgG had a higher specificity than the VDRL ELISA for
IgM. The sensitivity for
IgG and
IgM with 118 sera from patients with untreated
syphilis was 96.6 and 94.9%, respectively, which was equivalent to the sensitivities of the traditional nontreponemal tests. The performance of the VDRL ELISA was compared with that of an ELISA that uses
cardiolipin as the
antigen (
cardiolipin ELISA). The VDRL ELISA was significantly more sensitive (P less than or equal to 0.01) than the
cardiolipin ELISA with 25 sera from
syphilis patients but was less sensitive (P less than or equal to 0.01) with 53 sera from patients with
autoimmune diseases. The antibody reactivity in the VDRL ELISA could not be absorbed out by
lecithin and
cholesterol, and the sera from patients with
syphilis did not react in an ELISA that uses
cholesterol and
lecithin as the
antigen. This indicates that
cholesterol and
lecithin, although not antigenic by themselves, may change the structural form of the
epitope on
cardiolipin so that it becomes more recognizable for
antibodies in
syphilis and less recognizable for
antibodies in
autoimmune diseases. The results of the VDRL ELISA were expressed in percentages of the absorbance value of a positive control. The VDRL ELISA gave, without titration of sera, quantitative results that correlated with the quantitative results of the traditional nontreponemal tests obtained by titration. The VDRL ELISA will be well suited for large-scale testing for
syphilis and may replace other nontreponemal tests.