Human immunoglobulin germline alpha(IgA) transcripts are expressed in vivo and their level correlates to class switching.

Immunoglobulin isotype switching is preceded by transcription of exons located 5' of the immunoglobulin switch regions. These exons are referred to as 'I-exons' and transcription of these regions is believed to be an essential step in switch recombination. Such mRNA species lack a variable portion and are denoted 'germline' transcripts. We have previously identified I-regions in man and we have now investigated the in vivo expression of human germline transcripts. Germline alpha transcripts (containing an I alpha exon) were expressed in various lymphoid organs, including peripheral blood mononuclear cells. Decreased levels of germline transcripts were found in immunoglobulin deficiency diseases. These findings are compatible with an in vivo role of germline transcription in isotype switching and may contribute to the understanding of mechanisms underlying deficiency diseases.