The cellular and cytokine dynamics of reactions triggered by atopy patch testing with house dust mites were studied in six high-IgE beagles. Sites were scored and biopsied at 6, 24, 48, and 96 h, and samples were processed for histopathology, immunohistochemistry, and polymerase chain reaction (PCR).
All dogs developed positive reactions at some point in time. Mean clinical scores were significantly higher than baseline at 24, 48, and 96 h. Clinically, one of six dogs had a positive reaction at 6 h; two of six reacted at 24 and 48 h, and five of six at 96 h.
Histologically, superficial perivascular mononuclear and granulocytic dermatitis developed (5/6) after 6 h, and progressed in severity at 24 h (6/6). Additionally, at 48 h epidermal spongiosis, hyperplasia and pustules developed (5/6), and were marked at 96 h (6/6). At and beyond 6 h, progressive CD1c-positive epidermal Langerhans cell hyperplasia with cluster formation and dermal dendritic cell infiltration was noted. Cutaneous infiltration of CD3-positive T lymphocytes with epidermal clusters developed over time.
mRNA expression for the cytokines gamma-interferon (γ-IFN), interleukin-6 (IL-6), IL-12p35, IL-13, IL-18, and thymus and activation regulated chemokine (TARC) exhibited significant increases during the challenge compared to baseline, but there was no appreciable alteration in expression for tumour necrosis factor-alpha (TNF-α), IL-12p40, IL-10, regulated on activation normal T-cell expressed and secreted (RANTES), IL-5, IL-2, IL-4, and IL-8. No correlation was detected between clinical scores and cytokines. It is concluded that IL-6 plays a role in early reactions followed by an increase of TARC and IL-13, while IL-18 progressively increases in later reactions.