Classical Serological Reactions

The standard, or classical, serological reactions for syphilis have become firmly established in the practice of the public health system. They are used for making the diagnosis of the disease (as an auxiliary method of examination in the presence of clinical manifestations of the disease and in the detection of T. pallidum in syphilitic lesions, and as the principal method in the latent form of syphilis). They also play an important role in appraising the efficacy of antisyphilitic therapy: the physician appraises the quality of treatment by the given method from the rate of negative reversal of the serological reactions. With other indices the reactions are also taken into account as a criterion of complete cure. Finally, serological examination is carried out of individuals applying for employment at children's and at catering establishments and at other places of this kind. The tests are also conducted regularly in persons employed at these establishments. Serological examination is compulsory for donors and patients admitted to somatic hospitals (neurological, psychiatric, for internal diseases, etc.).

The standard serological reaction includes Wassermann's reaction (with different antigens). Besides, Kolmer's test (Wassermann's reaction in cold) has been given wider application recently. The Wassermann reaction and Kolmer's tests are carried out in two variants (qualitative and quantitative methods).

The great variety of standard serological reactions is explained by the proved antigenic mosaic character of T. pallidum and the resultant presence of the correspondingly numerous antibodies in the blood serum of a syphilitic patient (reagins, complement-fixating protein and polysaccharide antibodies, agglutinins, immobilizins, antibodies causing immune fluorescence, etc.). Different antibodies may predominate in each stage of syphilis and, consequently, reactions with some antigens may already be positive while with others they may still remain negative. Moreover, the relative specificity of the standard serological reactions obliges not just one but a complex of reactions to be carried out so as to avoid diagnostic errors. It should be borne in mind that the entire complex may produce a false positive, non-specific result in some cases. Positive serological reactions in blood are encountered in malaria, typhus, relapsing fever, leprosy, brucellosis, pneumonia, scarlet fever, malignant new growths, during menstruation, two weeks prior to and two weeks after delivery, after taking alcohol, fatty foods and some drugs, in chronic pyogenic processes, diseases of the liver, etc. The number of false positive non-specific results of standard serological reactions increases with age. All this calls for extraordinary caution in interpreting the results of serological examination in some cases and to regard these reactions as valuable auxiliary procedures verifying the clinical picture, the results of other laboratory tests (for T. pallidum, cerebrospinal fluid), and the results of confrontation.

Wassermann's reaction is known for its complexity; it is conducted in a special serological laboratory. The reaction is based on the complement-fixation phenomenon. Both specific antigens of T. pallidum and non-specific antigens (extracts from organs of healthy animals, e.g. muscles of beef heart) are used. Fixation of complement by a complex (lipoid antigen and reagin of the serum tested) occurs. A hemolytic system (sheep erythrocytes and hemolytic serum) is used for indication of the complex formed. Wassermann's reaction is more sensitive when it is made with the cardiolipin antigen. The modified Wassermann reaction in the cold (Kolmer's test) also proved to be more sensitive. Kolmer's test is distinguished by double-phase temperature regimens (the first phase—at 18-20⁰ C for 30 minutes, the second phase—in a refrigerator at +4 to -6^oC for 18-20 hours) under which fixation of complement takes place. Kolmer's test demonstrates reagins in sera in which Wassermann's reaction produces a negative result because of the low concentration of the reagins in them. Most syphilologists, however, claim that Kolmer's test and Wassermann's reaction with the cardiolipin antigen are more sensitive but less specific than the other modifications of Wassermann's reaction. That is why the physician should adopt a cautious approach to isolated positive results of Kolmer's test and Wassermann's reaction with the cardiolipin antigen.

In sharply positive results of these tests they are repeated with diminishing doses of the patient's serum so as to determine the reagin titre. The quantitative test for reagins helps in differentiating early and late latent syphilis and makes it easier to appraise the efficacy of antisyphilitic therapy: a decrease in the reagin titre testifies to the efficacy of treatment.

The degree of positivity of 'Wassermann's reaction, Kolmer's test is designated as follows: 4+ (sharply positive), 3+ (positive), 2+ or 1+ (weakly positive), ± (doubtful), - (negative). In quantitative Wassermann's reaction or Kolmer's test that serum dilution with which the reaction still produces a sharply positive result is recorded (e.g. 1: 5, 1: 10, 1: 20, etc. 1: 320). It has already been pointed out that Wassermann's reaction, however, can also produce a non-specific result (particularly with the use of the cardiolipin antigen and when the reaction is conducted in the cold).

In other countries more often, screening test for syphilis such as nontreponemal serologic tests for syphilis, usually a rapid plasma regain (RPR) or a Venereal Disease Research Laboratory (VDRL) test, is ordered. Nontreponemal serologic tests for syphilis detect antibodies to regain, a cholesterol-lecithin-cardiolipin antigen that cross-reacts with antibodies present in the sera of patients with syphilis. These antibodies are not specific for syphilis and should always be confirmed by a specific test for syphilis.

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