Evaluation of the usefulness of lymphocyte proliferation assays in the diagnosis of allergy to cow's milk.

BACKGROUND

The significance of cell-mediated mechanisms in IgE-mediated milk allergy (IgE-MA) and in milk-induced enterocolitis syndrome (ME) is controversial. Some investigators have claimed that lymphocyte proliferation assays are useful in the diagnosis of food hypersensitivity, despite the great variability in study designs and results reported. This study was undertaken to address many of these variables and to determine whether lymphocyte proliferation assays correlate with clinical diagnoses.

METHODS

Lymphocyte proliferative responses to milk antigen were evaluated in two groups of children, 27 with IgE-MA, and nine with ME and in 21 pediatric control subjects. IgE-mediated food allergy was documented by positive double-blind, placebo-controlled food challenges and positive skin prick test results. ME was diagnosed by oral challenge or by a history of repeated episodes of delayed vomiting (>2 hours) after ingestion of milk and by negative skin prick test responses. Peripheral blood mononuclear cells were isolated and cultured. Cultures stimulated with milk (the food antigen of interest), soy antigen (a nonrelevant food antigen), or tetanus antigen (a positive control antigen) and unstimulated controls were performed in quadruplicate. On days 5, 7, and 9, cells were pulsed with tritium-labeled thymidine and incubated for 4 hours. Results were compared as counts per minute (cpm) and as stimulation indices (SIs).

RESULTS

Maximal proliferation was generally seen on day 7. The median cpm (20,941) and the median SI (19.2) in response to milk antigen in the 27 children with IgE-MA were significantly greater than those in the control patients (6969 cpm; SI = 14.2; p = 0.001 and p < 0.05, respectively). However, the ranges were large and overlapped extensively (IgE-MA, 5616 to 52,053 cpm; controls, 469 to 39,260 cpm). The non-soy-allergic patients with IgE-MA also had a significantly greater response to soy antigen than did the control subjects when cpm were compared (0.01 < p < 0.05). There were no differences in background or in response to tetanus antigen. The median response to milk in the patients with ME (11,975 cpm) was significantly greater than that in control subjects (6969 cpm; 0.01 < p < 0.05), when cpm were compared but not when SIs were compared. There were no significant differences between the patients with IgE-MA and those with ME.

CONCLUSION

Overall, these results indicate that lymphocyte proliferation assays are neither diagnostic nor predictive of clinical reactivity in individual patients with milk allergy. Lymphocytes of many control patients are highly responsive to milk antigens, and lymphocytes of many patients with milk allergy are not. Statistically significant differences are only evident when the patients are compared as groups.