What type of antibody-like substance is used in the rapid plasma regain (RPR) card test

reagin type antibody.

Explanation:

The rapid plasma reagin test is a test used to diagnose syphilis.

Syphilis is a sexually transmitted disease which is caused by treponema pallidum.

The rapid plasma reagin test is not for measuring the antibodies against actual bacteria but for measuring the antibodies formation due to material released because of tissues damaged by treponema pallidum like IgG and IgM against lipodial materials which is released from damaged cells.