Identification of feline erythrocyte antigen 6 and lack of alloimmunization to feline erythrocyte antigen 4 in cats

Abstract

Background: New feline erythrocyte antigens (FEAs) have been described based on the presence of naturally occurring alloantibodies (NOAb), but their immunogenicity and clinical relevance are poorly understood.

Hypothesis/objectives: Describe the immunogenicity of FEA 4 after sensitizing FEA 4-negative cats lacking NOAb and characterize anti-FEA 4 alloantibodies produced, including their rate of appearance, agglutination titer, and immunoglobulin class.

Animals: Nineteen healthy type A cats were blood typed for FEAs 1 to 5 to identify suitable donor-recipient pairs for FEA 4 sensitization.

Methods: Four FEA 4-negative cats were transfused with FEA 4-positive red blood cells. Using a gel column technique, posttransfusion samples were screened daily for a week, weekly for a month, and monthly thereafter for anti-FEA 4 alloantibodies.

Results: Alloantibodies were not detected in the first 3 recipients despite repeated transfusions (1 and 3 additional transfusions for 2 and 1 recipients, respectively). In the 4th recipient, alloantibodies against its donor red blood cells were detected 21 days postsensitization. However, they were not directed against FEA 4, but rather against a novel FEA not yet described. The alloantibodies, named anti-FEA 6, remained detectable for >4 months after sensitization and were determined to be mostly immunoglobulin M based on sulfhydryl treatment.

Conclusions and clinical importance: Feline erythrocyte antigen 4 does not appear to be immunogenic because repeated sensitization of 4 cats failed to produce detectable anti-FEA 4 alloantibodies. A new immunogenic antigen, named FEA 6, has been discovered, but additional studies are needed to document its clinical importance.

Keywords: blood transfusion; crossmatch; feline erythrocyte antigen; immunogenicity.

FIGURE 1

The gel column technique employed to assess the presence of anti–FEA 4 alloantibodies in recipient 4 (FEA 4 negative) plasma on day 21 posttransfusion: The auto‐control, that is, recipient 4 plasma with its own RBC is negative, while a 2+ positive agglutination reaction is noted against the donor 1 RBC (FEA 4 positive). However, a negative reaction is present against the positive control (FEA 4+), while 2+ positive reactions are noted against 2 negative controls (negative controls 1 and 2; FEA 4−). FEA, feline erythrocyte antigens; RBC, red blood cells.

FIGURE 2

Anti–FEA 6 agglutination titers over time of recipient 4. The red arrow represents the day of the blood transfusion. FEA, feline erythrocyte antigens.