The invention concerns the use of at least one polypeptide comprising a protein fragment to obtain a diagnostic, prognostic, prophylactic or therapeutic composition for detecting, preventing or treating a pathological condition associated with a degenerative and/or neurological and/or autoimmune disease, said protein being selected among the proteins whereof the peptide sequence in native state corresponds to SEQ ID No 1, SEQ ID No 2, SEQ ID No 3, SEQ ID No 4, SEQ ID No 5, SEQ ID No 6, SEQ ID No 7, SEQ ID No 8, SEQ ID No 9, SEQ ID No 10, SEQ ID No 11, SEQ ID No 12, SEQ ID No 13, SEQ ID No 14, SEQ ID No 15, SEQ ID No 16, SEQ ID No 17, SEQ ID No 18, SEQ ID No 19, SEQ ID No 20, SEQ ID No 21, SEQ ID No 22, SEQ ID No 23, SEQ ID No 24, SEQ ID No 25, SEQ ID No 26, SEQ ID No 27, SEQ ID No 28, and SEQ ID No 29, and the peptide sequences having at least 70% identity, preferably at least 80% identity and advantageously at least 98% identity with any one of the peptide sequences SEQ ID No 1 to SEQ ID No 8 and SEQ ID No 10 to SEQ ID No 29, and the peptide sequences or fragments of said sequences belonging to a common family of proteins selected among perlecan, the precursor of the retinol-binding plasmatic protein, of the GM2 activator protein, of calgranulin B and of saponin B.