What type of antigen is used in the RPR card test?

The RPR (Rapid Plasma Reagin) card test is designed to detect the presence of non-treponemal antibodies, which are typically produced in response to the lipid antigens released from damaged host cells, particularly in the context of syphilis infection. The main antigen used in this test is cardiolipin, which is derived from heart tissue and is used in combination with lecithin and cholesterol to enhance its sensitivity and specificity as a test antigen.

In the RPR test, the cardiolipin leads to an agglutination reaction when mixed with the patient's serum containing reagin antibodies. A visible change (such as the formation of clumps) indicates a positive result, suggesting possible syphilis infection. The reliance on cardiolipin as the test antigen is essential because it is a key component responsible for the serological response being measured.

The other choices highlight different types of antigens or components that are not relevant to the RPR test. Live or killed treponemal organisms are associated with treponemal tests, which detect specific antibodies against the Treponema pallidum bacteria directly, while tanned sheep cells are utilized in other types of serological testing but not in the RPR specifically