Identification of a natural soluble form of human CD5.
CD5 is a 67 kDa type I glycoprotein which belongs to the Scavenger Receptor Cysteine-Rich (SRCR) family of receptors. This family includes either cell-surface (e.g. CD6) or secreted (e.g. Spalpha) proteins implicated in the development of the immune system and the regulation of immune responses. In this study, we purified and characterised a circulating natural soluble CD5 form (nsCD5) which is indistinguishable (in apparent molecular mass, glycosylation pattern, and antibody reactivity) from a recombinant soluble CD5 form (rsCD5) composed of the three extracellular SCRC domains. The nsCD5 is a N-glycosylated 52 kDa molecule present in normal human serum and in supernatants of in vitro phorbol ester- and CD3-stimulated peripheral blood mononuclear cells. The nsCD5 concentration in sera from healthy donors is relatively low (median 1.75 ng/ml, rn=166) and is similar to that found in sera from patients suffering of various autoimmune (systemic lupus erythematosus, primary Sjogren syndrome, rheumatoid arthritis) and non-autoimmune (chronic renal failure, B-cell chronic lymphocytic leukemia) disorders. In vitro experiments indicate that nsCD5 is released by proteolytic cleavage of the membrane form. These results represent the first evidence of proteolytic release of a transmembrane SRCR family member following cell activation.
Calvo
J
J
Servel d'Immunologia, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Hospital Clínic, Barcelona, Spain.
Places
L
L
Espinosa
G
G
Padilla
O
O
Vilà
J M
JM
Villamor
N
N
Ingelmo
M
M
Gallart
T
T
Vives
J
J
Font
J
J
Lozano
F
F
D000818:Animals; D015153:Blotting, Western; D018956:CD5 Antigens / Q000097:blood* / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000737:chemistry; D051379:Mice; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D012995:Solubility
D018956:CD5 Antigens; D011994:Recombinant Proteins