Abstract: The present invention relates to a method for diagnosing neurodegenerative processes in the CNS, such as Alzheimer's disease, by measuring syndecan-3 expression from monocytes isolated from the systemic circulation with antibodies and ligands specific to any portion of the 442 amino acid long protein core of syndecan-3.

Abstract: The invention relates to agents that inhibit the binding of SARS-CoV-2 to SDCs or the endocytosis of SARS-CoV-2 with SDCs for use in the treatment of SARS-CoV-2 infection by inhibiting the cellular entry of SARS-CoV-2 and/or the SARS-CoV-2-induced inflammatory response. The invention relates further on to a method of inhibiting SARS-CoV-2 infection, the cellular entry of SARS-CoV-2, and the SARS-CoV-2-induced inflammatory response comprising contacting the SARS-CoV-2 target cells with an agent that inhibits the binding of SARS-CoV-2 to SDC or the endocytosis of SARS-CoV-2 with SDCs. The agent as SDC-specific mono- or polyclonal antibody used may be a. an antibody specific for the human SDC isoforms (SDC1, -2, -3, -4), or b.

Abstract: The invention relates to a method for brain targeted delivery of macromolecular protein or peptide ligands, including mono- or bispecific antibodies, nanobodies and active ingredients possessing specificity for 45 to 384 amino acid region of the SDC3 core protein into the brain, by a.) attaching the mono- or bispecific SDC3 antibody, nanobody, or mono or bispecific macromolecular ligands via systemic circulation to 45 to 384 amino acid region of SDC3 expressed on endothelial cells of the blood-brain-barrier, or b.) conjugating an active ingredient to an SDC3 specific mono- or bispecific antibody, nanobody, or mono or bispecific macromolecular ligands, and attaching the conjugate via systemic circulation to SDC3 expressed by endothelial cells of the blood-brain-barrier. Furtheron the invention relates to the use of a syndecan-3 target antibody, nanobody or macromolecular ligand, alone or in association with an active ingredient, as a therapeutic agent for treating neurodegenerative or metabolic disorders.