Drugs and metals are examples of xenobiotics that can induce hypersensitivity in humans. These adverse reactions are classified as allergy if repeated exposure leads to the same type of clinical manifestation. Together with the clinical history, the skin test is the most commonly used test for the diagnosis of allergic disease. However, in vivo testing per se has drawbacks such as the risk of potentiation of the allergy or even sensitisation to a given test substance. For this reason in vitro testing is an attractive diagnostic alternative since it does not involve any exposure of the test subject to the allergen.
The lymphocyte transformation test (LTT) has been used to complement the diagnosis of allergy to drugs and metals for more than thirty years. The principle behind this test is to show the presence of allergen-specific memory lymphocytes in peripheral blood, which is a sine qua non of a true allergy. LTT reveals the proliferation of such cells by showing DNA synthesis as the uptake of 3H-thymidine in primary PBMC (peripheral blood mononuclear cell) cultures treated with the allergen. However, LIT has not yet been generally accepted as a stand-alone test in the diagnosis of allergy. One reason for this is that different chemical properties of the allergens may lead to either false positive or false negative LTT responses.
In the present study we investigated allergy to the drug bacampicillin and to the metals Au, Pd, Ni and Hg. Three different protocols for LTT: LIT in micro cultures (LTT-micro), LTT in macro cultures (LTT-macro) and memory lymphocyte immunostimulation assay (MELISA) were compared using a skin test or clinical history as reference methods. LTI showed a sensitivity of 87% and a specificity of 90% when used in the diagnosis of allergy to bacampicillin. When allergy to Au, Pd, Ni and Hg was investigated, the sensitivity was 33- 95% and the specificity 0-79%. There were no significant differences between the test protocols, except that MELISA showed a significantly higher specificity than LTT-micro and LTT-macro when Hg2+ was used as antigen. Even so, this specificity was only 70%, which would result in 30 of 100 healthy subjects receiving a false diagnosis of Hg allergy when using the MELISA protocol. Ni2+ also induced high numbers of false-positive LTI responses, 77-85% patch-test negative subjects showed positive results to these metals. However, group comparisons showed a significantly higher proliferation intensity in allergic than in nonallergic groups for all allergens except Hg2+. Furthermore, only 56% of patients with verified allergy to mercury showed a positive MELISA, a sensitivity that is unacceptably low.
Following these findings, we investigated whether other endpoints than DNA synthesis could be used to discriminate allergic from healthy subjects, using primary PBMC cultures with Hg2+ or Ni2+ as a model system. Analysis of the T-cell receptor Vß profiles of lymphoblasts induced by these metal ions showed individual patterns, and there was no difference between healthy and allergic groups. However, the fraction of CD4+/Vß2+ cells correlated significantly with the proliferation intensity induced by Hg2+ in patients with a verified Hg allergy but not in non-allergic controls. Interestingly, such a correlation was not seen with CD8+/Nß2+ cells. This indicates that Hg2+ does not function as a superantigen, since classical superantigens also stimulate CD8+ lymphocytes. When Ni2+ was used as antigen we found significantly higher IL-10 production in allergic than in non-allergic subjects, despite no significant difference in proliferation intensity between these two groups.
In conclusion, the LTT test is useful for the diagnosis of allergy to bacampicillin. Regarding Au, Pd and Ni the LIT has low validity and can only be used to discriminate groups of allergic from non-allergic individuals. LTT with Hg2+ and Ni2+ is not useful for the diagnosis of allergy to these metals since a high fraction of non-allergic individuals show positive results, irrespective of the test protocol used. This thesis calls for further studies on the usefulness of in vitro IL-10 production for the diagnosis of Ni allergy as well as on the specificity of in vitro induced CD4+N~2+ lymphoblasts from Hg allergic subjects.
Linköping: Linköpings universitet , 2000. , 69 p.
2000-03-31, Berzeliussalen, Universitetssjukhuset, Linköping, 09:30 (Swedish)