Recombinant L1R protein induces cross-neutralizing antibodies against capripoxviruses despite a subdominant humoral response.

Capripoxviruses, including the goatpox virus (GTPV), sheeppox virus (SPPV), and lumpy skin disease virus (LSDV), cause substantial economic losses in domestic ruminants in Asia, Africa, the Middle East, and Europe. The identification of viral antigens that elicit protective immunity, along with the characterization of antigen-specific humoral responses, is crucial for the rational development of vaccines and serodiagnostic assays. L1R is an essential membrane protein of the intracellular mature virion (IMV) and a known neutralizing antibody target for poxviruses. In this study, a truncated L1R ectodomain (rL1RΔTM; 191 aa; 20.6 kDa) was expressed in Escherichia coli, purified under denaturing conditions via affinity chromatography, and subsequently refolded to yield an antigenically functional protein. The expression of the recombinant protein was confirmed using SDS-PAGE and Western blotting. Immunization of rabbits with purified rL1RΔTM (250 μg per dose) elicited antigen-specific IgG responses and generated cross-neutralizing antibodies against capripoxviruses. In contrast, the rL1RΔTM-based indirect ELISA, utilizing sera from naturally infected or vaccinated animals, demonstrated that L1R-specific antibodies represent only a minor component of the capripoxvirus-specific humoral response. Consequently, the rL1RΔTM ELISA exhibited high diagnostic specificity (98.7-100%) but limited sensitivity (26-39% in infected animals and 8-22% in vaccinated animals). Additionally, it showed a weak correlation with neutralization titers (R2 = 0.11-0.18). These findings demonstrate that the subdominant contribution of L1R to the natural humoral immune response limits its effectiveness as a standalone antigen for serodiagnosis. Nonetheless, L1R is a conserved immunogen capable of inducing cross-neutralizing antibodies against capripoxviruses, supporting its potential utility in the development of pan-capripoxvirus subunit vaccines and monoclonal antibody production.