Study Questions Validity of Skin Prick Test in Food Allergy Testing

Emma Hitt, PhD

March 11, 2003

March 11, 2003 (Denver) — In food allergy, the Th2 response generally thought to mediate allergic reactions may not be detectable, and Th1 cell-mediated immunity may play a pathogenic role, findings of a preliminary study suggest.

The findings indicate that patients who do not have a reaction to the skin prick test should not be ruled out as patients undergoing an allergic reaction, said presenter Jonathan Malka-Rais, MD, from the Department of Pediatrics-Immunology at Georgetown University Medical Center in Washington, D.C.

The researchers reported their findings here at the 60th meeting of the American Academy of Allergy, Asthma, and Immunology on Saturday.

Dr. Malka-Rais and colleagues investigated Th1 cytokine profiles and the presence of lymphoid nodular hyperplasia in 12 patients with food allergies confirmed by positive clinical symptoms and a double-blind placebo-controlled food challenge (DBPCFC). However, all of these patients produced a negative skin test/RAST.

A second group of four patients with celiac disease, a Th1-mediated disorder, was also included in the analysis.

All patients underwent lymphocyte cytokine profiling. Group 1 underwent ileal biopsies, and group 2 underwent jejunal biopsies.

In the first group, peripheral blood CD4 and CD8 lymphocyte distributions were normal, but CD4+ cells that displayed a decreased intracellular Th1 cytokine pattern predominated (mean interferon gamma was 3 ± 2 and interleukin-2 was 5 ± 3). By comparison, Th2 intracellular cytokine patterns were normal (mean interleukin-4 was 1 ± 1; interleukin-5 was 0.3 ± 0.7; and interleukin-10 was 0.1 ± 0.1).

The group with celiac disease also displayed normal CD4 and CD8 lymphocyte distributions, but this group showed a predominance of CD4+ cells with an increased intercellular Th1 cytokine pattern (mean interferon was 18 ± 11 and interleukin-2 was 20 ± 8), whereas the Th2 intracellular cytokine pattern was normal (mean interleukin-4 was 3 ± 1; interleukin-5 was 0.1 ± 0.1; and interleukin-10 was 0.2 ± 0.1).

Lymphoid nodular hyperplasia was found in each of the ileal biopsies of the 12 patients in group 1, but was not present in any of the jejunal biopsies from patients in group 2.

"The results of these studies not only suggest that Th1 cell mediated immunity may play a pathogenic role in some patients with non-IgE mediated food allergy but also that lymphoid nodular hyperplasia may be a hallmark histologic lesion in this group of patients," the researchers conclude.

"We tend to believe that those patients who do not have a reaction to the skin prick test have a non-IgE related disease," Dr. Malka-Rais told Medscape, "but this may not be the case and food allergy cannot be ruled out in these patients," he said.

He also noted that other researchers have speculated that a Th1 response may be involved in an allergic response, "and these findings, while preliminary, support that idea."

Kirsten Beyer, MD, an assistant professor and allergy specialist at the Mount Sinai School of Medicine, in New York City, noted that a study she was presenting at the same meeting contrasted with these results and that her study concluded that gastrointestinal food allergies were Th2 mediated.

"But we looked directly at mucosal lymphocytes in the gut," Dr. Beyer told Medscape. "This study looked at peripheral blood lymphocytes after short-term stimulation with allergens, so I'm not completely convinced that Th1 is involved based on these results.

"A skin-prick test evaluates levels of systemic IgE, but it does not rule out the presence of local IgE and a Th2-mediated reaction," she added.

AAAAI 60th Annual Meeting: Abstract 144. Presented March 8, 2003.

Reviewed by Gary D. Vogin, MD