The present invention is concerned with a fragment of IgA1-protease having 40 to 200 amino acid residues and comprising at least 40 amino acids of an amino acid sequence as shown in SEQ ID NO:1, beginning with the amino acid in any one of positions 1 to 5 and ending with an amino acid in any one of positions 40 to 104 or a homologous sequence, its use as a carrier for a conjugate, particularly in combination with a polysaccharide, and a process for producing the peptide as well as vaccines comprising said peptide.