Which of the following is most likely to yield a false-positive result in serological testing for syphilis in systemic lupus erythematosus?

Serological testing for syphilis often involves non-treponemal tests such as the Rapid Plasma Reagin (RPR) test. These tests detect substances that are not specific to the syphilis-causing organism but are instead markers of the body's response to cellular damage that can occur in various conditions, including autoimmune diseases like systemic lupus erythematosus (SLE).

In the case of systemic lupus erythematosus, patients may have elevated titers of antibodies that can react with the reagents used in non-treponemal tests, leading to a false-positive result. The presence of certain antibodies in SLE can mimic the reactivity that these tests are measuring, causing a positive result even in the absence of actual syphilis infection.

The other options listed do not primarily relate to syphilis serological testing. Cold agglutinins are associated with conditions like Mycoplasma pneumoniae infection and are not typically involved in syphilis testing. Heterophile antibodies are associated with infectious mononucleosis and can produce positive results in other tests but are not directly related to syphilis. The p24 antigen refers to the HIV virus and is not relevant to syphilis testing at all