Background: Activity-dependent neuroprotector (ADNP) is a neuroprotective molecule containing an 8-amino acid peptide, NAPVSIPQ (NAP), that is sufficient for its neuroprotective effects. Objective: To assess the expression of ADNP in the human immune system in normal subjects and multiple sclerosis patients. Materials and Methods: ADNP expression was assessed in peripheral blood mononuclear cells (PBMCs) from healthy donors and multiple sclerosis (MS) patients using staining with anti-ADNP (NAP) antibodies and markers for T cells, B cells, monocytes and natural killer cells. ADNP mRNA was determined in peripheral blood from MS patients (n = 24) and matched controls (n = 21). Expression of activation markers CD69 and CD154 and of IFN-γ was assessed by flow cytometry in stimulated PBMCs. Effects of NAP on immune cell proliferation was assessed by tritiated thymidine incorporation. Results: Monocytes, B cells and T cells, but not regulatory (CD4+CD25+) T cells expressed ADNP. NAP peptide decreased the expression of CD69, CD154 and IFN-γ in PBMC and caused suppressed anti-CD3-/anti-CD28-stimulated PBMC proliferation. ADNP mRNA was reduced in MS compared to control peripheral blood. Conclusion: ADNP is expressed in many immune system cells. ADNP mRNA is reduced in PBMCs in MS. The peptide NAP, which plays an important role in neuroprotection, has potential immunomodulatory properties.