a process for the detection of cpn10 in serum or other biological fluids including the steps of raising antibody to cpn10 ; reacting said antibody with a sample of biological fluid suspected of containing cpn10 ; and detecting the presence of cpn10 in said sample by a signal amplification resulting from production of a cpn10 - antibody complex . there is also provided a process for promotion of cell growth or immunosuppression including the step of administration of cpn10 to a mammalian subject . there is also provided recombinant cpn10 .