Prevalence of a Novel Immunogenic Feline Erythrocyte Antigen (FEA 6) and Expression Patterns Between FEAs

Abstract

Background: After the identification of five novel feline erythrocyte antigens (FEAs) and evidence establishing FEA 1's immunogenicity, attempts to sensitize a cat to FEA 4 unexpectedly resulted in the production of alloantibodies directed against an unknown antigen, named FEA 6.

Objectives: To estimate the prevalence of FEA 6 as a presumably new antigen, identify corresponding naturally occurring alloantibodies (NOAb), and investigate the associations between known FEAs.

Animals: Two hundread and seven cats.

Methods: Prospective blood typing for FEAs 1-6 was conducted in Type A cats (n = 193), followed by serial crossmatching in groups of 3-7 cats to detect NOAb and identify their target FEA. Agreement between FEA 6 blood typing and other FEAs was assessed. Associations between FEAs were evaluated to identify expression patterns.

Results: Among 193 Type A cats, 67% were FEA 6-positive. Agreement analyses were supportive of FEA 6 being distinct from FEAs 1-5. NOAb were detected in 11 cats (5.7%), none of which were anti-FEA 6. Only FEA 1-negative status was significantly associated with the presence of NOAb (OR = 6.6, 95% CI, 1.9-23.1; p < 0.001). Significant associations were observed between the expressions of FEAs 1 and 4 (χ² = 25.7, p < 0.001), and FEAs 3 and 5 (Fisher's exact test, p < 0.001), respectively.

Conclusions and clinical importance: The immunogenicity and prevalence of the newly discovered FEA 6 raise concerns regarding its clinical relevance and role in posttransfusion sensitization. FEA 1/FEA 4 and FEA 3/FEA 5 pairs might belong to distinct antigenic systems.

Keywords: Mik antigen; alloimmunization; blood typing; crossmatch; naturally occurring alloantibodies; transfusion.

FIGURE 1

Illustrative example of the method used for identifying the target antigen of newly detected naturally occurring alloantibodies based on crossmatch incompatibilities. Cat 33.6's plasma was found incompatible to all FEA 5‐positive cats in the pool (i.e., crossmatches between cat 33.6 and cats 33.1, 33.3, 33.4 and 33.5) and compatible to all FEA 5‐negative cats (i.e., crossmatch between cat 33.6 and cat 33.2). Given that this cat was FEA 5‐negative, its NOAb were likely directed against FEA 5. Besides, all other cats were compatible with each other (data not shown). −, negative (blood typing) or compatible (crossmatch); +, positive (blood typing) or incompatible (crossmatch); A/C, autocontrol; FEA, feline erythrocyte antigen. ^aResults ≥ 1+ were considered positive for blood typing, whereas results ≥ 2+ were considered incompatible for crossmatching.