Background The 33 kD component has been identified as a major allergen ofPenicillium citrinum, the most prevalent Penicillium species in the Taipei area of Taiwan.
Objective This study analyses the isoforms, antigenic cross-reactivity and the N-terminal amino acid sequence of the 33 kD allergen of P. citrinum.
Methods The composition of isoforms and antigenic cross-reactivity was analysed by SDS-PAGE and 2D-immunobIotting using MoAbs generated. The N-terminal sequence was analysed by using an automatic gas/liquid phase sequencer.
Results Two MoAbs (55A and 34H) against the 33 kD allergen were generated in the present study. In addition to the 33 kD component. MoAb 34H also showed immunoblot reactivity to other components in the crude extract of P. citrinum. Analysed by 2D-immunoblotting. at least six different isoforms of the 33 kD component with pl values ranging from 6.75 to greater than 7.0 were shown to be reactive to both MoAbs and IgE antibodies in serum of an asthmatic patient. Different immunoblot patterns were observed when both MoAbs were reacted with four different strains of P. citrinum used in the present study. Among another six different Penicillium and four different Aspergillus species tested, only an immunoblot reactivity of MoAb 55 A to the 33 kD component of P. brevicompactum was observed. In 2D-immunoblotting. components of P. brevicompactum with an MW of about 33 kD and pi values similar to those of the 33 kD component of P. citrinum reacted with MoAb 55A and IgE antibodies in serum of the asthmatic patient. The N-terminal amino acid sequence of the 33 kD component of P. citrinum was determined to be ANVVQSNVP which was identical to the first 9 N-terminal amino acids of a heat-labile alkaline serine proteinase from P. citrinum.
Conclusion Results obtained in the present study suggest that the 33 kD major allergen of P. citrinum may be an alkaline serine proteinase.