In vitro lymphocyte proliferation in the diagnosis of allergy to phenoxymethylpenicillin

Background The aim of this study was to investigate in vitro lymphocyte pro liferation in the diagnosis of allergy to phenoxymethylpenicillin (PcV), co mparing chemically reactive PcV, added to cell cultures in unconjugated for m, to a PcV-PLL (poly-L-lysine) conjugate as antigens. Side-chain specifici ty of lymphoproliferative responses was investigated with reactive benzylpe nicillin (PcG) and bacampicillin. Methods Seventeen patients with a history of hypersensitivity reactions in connection with PcV treatment were studied by means of the lymphocyte trans formation test (LTT), the radioallergosorbent test (RAST), skin tests (pric k and intracutaneous), and oral challenge with PcV. LTT was also performed in 20 control subjects exposed to PcV therapeutically, and in eight subject s with occupational exposure to this penicillin. Results Nine patients had a positive in vivo test to PcV (five by oral chal lenge, three by intracutaneous test, and one by both tests), and six were c hallenge-negative. When reactive PcV was used as antigen in LTT, positive L TT responses were observed in five of the nine patients with a positive in vivo test, and two of them were also side-chain specific. Positive LTT resp onses with reactive PcV also correlated with a positive RAST in five of sev en subjects. None of the six patients with a negative challenge test, and o nly one of the 28 controls showed a positive LTT result with reactive PcV. Thus, the specificity of LTT with reactive PcV was 96%. In contrast, when P LL-conjugated PcV served as antigen, four challenge-negative subjects and 1 1 controls were LTT-positive. Conclusions The results of this study indicate that LTT with chemically rea ctive PcV could be useful as an in vitro complement in the diagnosis of PcV allergy and as a tool to reveal the side-chain specificity of peripheral b lood lymphocytes. A positive LTT to PLL-conjugated PcV may be an indicator of immunization, but not necessarily allergy, to the penicilloyl structure.