Tuftsin is a tetrapeptide (Thr-Lys-Pro-Arg, TKPR) located in the Fc-domain of the heavy chain of immunoglobulin G (residues 289-292).

The leukokinin-S so nicked is present in tissues and blood, free or bound to outer membrane of the appropriate phagocyte.

The membrane enzyme leukokininase acts on the bound leukokinin-S to cleave it at the amino end of threonine between residues 288 and 289 (-Lys-Thr-).

Leukokininase can be found on the outer membrane of phagocytic cells: blood neutrophil leukocytes of human and dog, rabbit peritoneal granulocyte.

[2] Injection of tuftsin intraperitoneally increases the formulation of TNF in serum and supernatants of cultured splenic and peritoneal adherent cells.

[2] The enhancement of antitumour immune response by immunomodulators is capable of stimulating reticuloendothelial and T-cell-mediated tumour destruction.

In a phase I study, tuftsin was shown to be nontoxic in adult human patients with advanced cancer when it was injected once intravenously (0.96 mg/kg body weight).

[2] Tuftsin deficiency can be hereditary[1] or can occur following splenectomy, resulting in increased susceptibility to certain diseases e.g.: infected eczematous dermatitis with draining lymph nodes, otitis and sinusitis.

Conjugates with polytuftsin retain tuftsin-like effects and increase the epitope specific antibody production.

Tuftsin sequence appears in residues 9-12 from the amino terminal of p12 protein of Rauscher murine leukemia virus.

Lys-Pro-Pro-Arg (KPPR) is also an inhibitor of phagocytosis, superoxide anion production and chemotaxis both human and rat PMN leukocytes and monocytes.