The mouse macrophage activation-associated marker protein, p71/73, is an inducible prostaglandin endoperoxide synthase (cyclooxygenase).

The inducible protein p71/73 marks the response of mouse macrophages to one of several stimuli (e.g., bacterial lipopolysaccharide or poly I:C) that trigger the expression of cytolytic activity when these cells have previously been primed for tumor cell killing by interferon-gamma (IFN-gamma). The results reported here identify this marker protein as the inducible prostaglandin endoperoxide synthase (PES), TIS10/PES-2. Identification was based on four findings: (1) p71/73, like the TIS10/PES-2 protein, was associated with cellular membranes; (2) the sequence of amino acids in the NH2 terminus of both p71 and p73 was 96% identical to the predicted NH2-terminal sequence of the TIS10/PES-2 protein; (3) a polyclonal antiserum raised against the COOH-terminal region of the TIS10/PES-2 gene product recognized p71/73 in immunoblots; and (4) dexamethasone, which blocks induction of TIS10/PES-2 expression, inhibited the induction of both p71/73 synthesis and tumoricidal activity in macrophage. Several regulatory roles for this protein in the activation process are possible.