Expression of a C-reactive protein neoantigen (neo-CRP) in inflamed rabbit liver and muscle.

We have reported that human C-reactive protein (huCRP) can exist in two antigenically distinct forms which are observed as the native, pentameric, phosphorylcholine (PC)-binding CRP ("native-huCRP antigen"), and as a conformationally and physicochemically distinct free huCRP subunit ("neo-huCRP antigen"), respectively. We have demonstrated that forms of huCRP which preferentially express neo-huCRP antigenicity are naturally present on the surface of both normal human peripheral blood B lymphocytes and lymphocytes with natural killer cell activity. We have also reported that forms of huCRP expressing the neo-huCRP antigen have potent in vitro activities in platelet, polymorphonuclear leukocyte, and monocyte assays. In this study, we demonstrate a rabbit-CRP (raCRP) neoantigen can be expressed when isolated PC-binding raCRP is modified in analogy to huCRP. This "neo-raCRP" is cross-reactive with the neo-huCRP antigen and occurs naturally in acute phase but not normal rabbit liver and muscle. The relative distribution and localization of both antigens were comparable in tissue sections taken at 24 and 48 hr postinflammation elicited with typhoid vaccine. These data support the concept that CRP molecules expressing a structure and antigenicity which are distinct from native, pentagonal CRP do occur in vivo, and that such molecules accumulate at tissue sites of inflammation and necrosis.