Abstract: The invention features attracting polypeptides and nucleic acids encoding them. The attractin polypeptides are useful for enhancing immune responses.

Abstract: A soluble form of CD26 isolated from human serum is disclosed. The serum form shares similar enzymatic and antigenic properties with the membrane form. However, in several biochemical aspects there are distinct differences. In particular, the soluble serum form has a molecular weight of 175 kDa (in contrast to the 105 kDa molecular weight of the membrane form), and it does not bind Adenosine Deaminase Type-1. Nevertheless, the soluble form expresses functional dipeptidylpeptidase IV activity and retains the ability to costimulate the T lymphocyte response to recall antigen. Although 105 kDa membrane type CD26 may be found in the serum in small amounts, the majority of serum DPPIV activity is provided by a novel peptidase structurally distinct from membrane C26/DPPIV.

Abstract: A circulating, soluble form of DPPIV/CD26 isolated from human serum is disclosed. The serum form shares similar enzymatic and antigenic properties with the ubiquitous membrane form. However, in several biochemical aspects there are distinct differences. In particular, the circulating serum form has a molecular weight of 175 kDa (in contrast to the 105 kDa molecular weight of the membrane form), and it does not bind Adenosine Deaminase Type-1. Nevertheless, the circulating form expresses functional dipeptidylpeptidase IV activity and retains the ability to costimulate the T lymphocyte response to recall antigen. Circulating DPPIV has been determined to be the soluble form of a 175 kDa DPPIV CD26-related molecule rapidly expressed on the surface of activated T cells, prior to the expression of 105 kDa CD26. Although 105 kDa membrane type CD26 may be found in the serum in small amounts, the majority of serum DPPIV activity is provided by a novel peptidase structurally distinct from 105 kDa CD26/DPPIV.