Prevalence of serum immunoglobulin E against cross-reactive carbohydrate determinants in allergic and nonallergic horses, and its impact on polysensitisation in serum allergen tests.

Many horses, whether allergic or not, have IgE antibodies that recognize shared carbohydrate structures on allergens, which can make blood allergy tests look falsely positive for many items. Adding a blocker for these carbohydrate determinants reduced the number of apparent sensitivities.

What are cross-reactive carbohydrate determinants (CCDs)?

• CCDs are carbohydrate motifs on many plant and insect glycoproteins that IgE can recognize across unrelated allergen sources.
• Because these motifs are shared, IgE against CCDs can bind multiple allergens in vitro, creating broad panels of positives that may not reflect true, clinically relevant sensitization.
• The result is reduced specificity of serum allergen tests, with “polysensitisation” (many positives) that may be artifactual.

Study goals

• Determine how common anti-CCD IgE is in horses with clinical allergy compared with nonallergic horses.
• Assess how anti-CCD IgE influences polysensitisation on serum allergen testing and whether a CCD-blocking reagent can reduce spurious positives.

Study design and methods

• Population: 42 horses total, comprising 21 allergic and 21 nonallergic animals.
• Anti-CCD detection: Sera tested for anti-CCD IgE using a commercial CHO enzyme-linked immunosorbent assay (ELISA).
• Allergen-specific testing: A serum allergen-specific Fc-ε receptor ELISA was used to quantify sensitization patterns across allergen groups (e.g., grasses, weeds, mites, stinging insects).
• Intervention: The allergen ELISA was run with and without a proprietary anti-CCD blocking solution to gauge its effect on the number of positive results.
• Outcome definition: Polysensitisation was the count or breadth of positive specific IgE results across the allergen panel.
• Statistics: Group comparisons included allergic versus nonallergic horses and anti-CCD–positive versus –negative horses; significance assessed at the 95% confidence level with reported p-values.

Key results

• Prevalence: Anti-CCD IgE was detected in 30 of 42 horses (approximately 71%).
• Group comparison: No significant difference in anti-CCD prevalence between allergic and nonallergic horses (p = 0.18), indicating anti-CCD IgE is common regardless of clinical allergy status.
• Impact on test profiles: Horses with anti-CCD IgE showed greater polysensitisation on serum allergen tests than those without anti-CCD IgE across all allergen groups except mites.
• Statistical significance: The increase in polysensitisation among anti-CCD–positive horses was significant for grasses (p < 0.03), weeds (p = 0.02), and stinging insects (p = 0.0005), and this pattern held in both allergic and nonallergic groups.
• Blocking effect: Adding the anti-CCD blocker produced an average 43% reduction in polysensitisation, consistent with removal of CCD-driven, non-specific binding.

Interpretation and implications

• Anti-CCD IgE is common in horses, mirroring prevalence seen in pollen-sensitized humans, and is not a hallmark of clinical allergy by itself.
• The presence of anti-CCD IgE can inflate the number of positive serum allergen results, particularly for plant pollens and insect-related allergens, potentially misleading diagnosis and management.
• Using a CCD-blocking step can meaningfully improve the specificity of serum allergen tests by reducing artifactual positives and helping identify truly allergen-specific IgE.
• The lack of effect in mite allergens suggests these results may be driven more by protein epitopes or by different glycosylation patterns, though this mechanism was not tested directly.

Strengths and limitations

• Strengths: Inclusion of both allergic and nonallergic horses allows prevalence estimates independent of clinical status; within-sample comparison with and without CCD blocker strengthens causal inference about CCD interference.
• Limitations: Modest sample size; use of a single commercial anti-CCD assay and proprietary blocker limits generalizability; reliance on serum testing without clinical challenge outcomes means “true” clinical relevance of remaining positives was not confirmed; details of allergen panel composition and cutoffs were not provided in the abstract.

Practical takeaways for clinicians and laboratories

• Interpret broad panels of serum IgE positives in horses cautiously, especially to grasses, weeds, and stinging insects, where CCD-driven cross-reactivity is common.
• When available, request or perform CCD-blocked testing, or confirm key positives with additional methods and clinical history before formulating immunotherapy.
• Prioritize allergens that remain positive after CCD inhibition when selecting targets for avoidance strategies and immunotherapy.
• Communicate with diagnostic laboratories about CCD-blocking options and reporting formats that quantify polysensitisation before and after inhibition.

Future directions

• Replicate findings in larger, diverse equine populations and across different testing platforms and blockers.
• Directly correlate CCD-blocked test profiles with clinical outcomes, including response to allergen immunotherapy and environmental control measures.
• Map which equine-relevant allergen sources are most affected by CCD interference to refine panels and improve diagnostic algorithms.