The clinical and physiological aspects of tuftsin deficiency syndromes exhibiting defective phagocytosis

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Tuftsin: its chemistry, biology, and clinical potential

Tuftsin is a tetrapeptide, Thr-Lys-Pro-Arg, which resides in the Fc-domain of the heavy chain of immunoglobulin G. The peptide originates from a specific fraction of the parent protein through enzymatic processing. Tuftsin possesses a broad spectrum of activities related primarily to the immune system function and exerts on phagocytic cells, notably on macrophages. These include potentiation of various cell functions such as phagocytosis, motility, immunogenic response, and bactericidal and tumoricidal activities. The features of tuftsin, coupled with its low toxicity, make the peptide an attractive candidate for immunotherapy. Tuftsin's capacity to augment cellular activation is mediated by specific receptors that were identified, characterized, and recently isolated from rabbit peritoneal granulocytes. Tuftsin has been chemically synthesized by a variety of techniques, some of which are adequate for large-scale preparations. A multitude of analogs have also been synthesized and extensively studied for structure-function relationships.

Isolation and subunit composition of tuftsin receptor

Tuftsin (Thr-Lys-Pro-Arg) receptor was purified to apparent homogeneity by affinity chromatography, using a pentapeptide analog (Thr-Lys-Pro-Pro-Arg) that binds the receptor more than 4 times as avidly as tuftsin. The analog was covalently linked to a solid support (Affi-Gel 10). Rabbit peritoneal granulocyte membrane solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate was applied to the affinity column, the column was washed with 0.1 M ammonium carbonate (pH 7.9) and 0.1 M ammonium acetate (pH 5), and bound material was eluted with 20 nM tuftsin or pentapeptide. The eluate was concentrated and subjected to gel filtration; this yielded one major peak of [3H]tuftsin binding activity corresponding to approximately 500 kDa and a minor peak at approximately 250 kDa. Rechromatography of either peak resulted in the appearance of the same major and minor peaks. NaDodSO4/PAGE of the affinity-purified material under nonreducing conditions showed only two silver-staining bands. Electroblotting followed by [3H]tuftsin overlay and fluorography showed two adjacent radioactive bands corresponding in mobility to the silver-stained bands. Under reducing conditions, NaDodSO4/PAGE yielded molecular mass values 62 kDa and 52 kDa for the two tuftsin receptor subunits. Electron microscopy revealed a homogeneous population of spherical molecules with diameters of 104 A.

The uniqueness of protein sequences: molecular territoriality

The number of tripeptides which do not occur and which occur only a small number of times in the existing data bank of protein sequences is much larger than that expected on the basis of random selection (from Monte Carlo analyses). Forty tripeptides are not found in the data bank of 289 500 amino acids while the value expected on the basis of random selection is 8.0 +/- 3.1. Seventy-one tripeptides occur only once with an expected value of 37.1 +/- 6.1. These results suggest that some peptides not found in certain species are reserved for use only in other species. The proposal is made that small peptides serve as species specific markers and function as signals in the recognition process for activation of the immune response.

Administration route and splenectomy effects on resistance to pneumococci in rats

Normal and splenectomized rats were challenged with Streptococcus pneumoniae type 1 via different administration routes. In experiment I, previously splenectomized or sham-operated rats received 4 X 10(3) colony-forming units (CFU) of pneumococci via (i) a peripheral vein, (ii) subcutaneously, or (iii) intraperitoneally. The results indicated an increased susceptibility of the splenectomized animal to pneumococci administered via all three routes. However, subcutaneously administered pneumococci gave a lower mortality than pneumococci given intravenously or intraperitoneally. In experiment II 40 splenectomized rats received 4 X 10(3) CFU of pneumococci via (i) peripheral, (ii) portal, or (iii) caval veins or the aorta. No differences in mortality were found. In experiment III, non-operated animals received 4 X 10(5) CFU of pneumococci either intravenously or intraperitoneally, resulting in mortality rates of 0/20 and 17/20, respectively. After 2 weeks the rats surviving intravenous challenge received 4 X 10(5) CFU of pneumococci intraperitoneally; all survived. The data indicate the the spleen and the subcutis have a greater capacity to protect against pneumococci in the absence of specific antibody than the peritoneum or the circulation outside the spleen.

Antibacterial properties of tuftsin and its analogs

The antibacterial properties of tuftsin and its 11 analogs on 20 bacterial strains were investigated. Tuftsin showed a definite antibacterial effect at a minimal effective concentration of 62.5 micrograms/ml. All analogs were either less effective or lacked any activity. The bacteria used included some highly pathogenic organisms.

Tuftsin, a natural activator of phagocyte cells: an overview

The recognition that a small oligopeptide was responsible for the full stimulation effect of specific cytophilic gamma-globulin on blood neutrophils arose from a study of the kinetics of phagocytosis. These were unusual in that the stimulation was short lived and that preincubation of the phagocyte with the gamma-globulin rendered the latter inactive. The oligopeptide was isolated, its structure determined (Thr-Lys-Pro-Arg) and synthesized. The discovery of human mutants with tuftsin deficiency exhibiting signs and symptoms of frequent severe infection further emphasized the specific biological function of the tetrapeptide. The mutant peptide was isolated, sequenced (Thr-Glu-Pro-Arg), and synthesized. Further studies showed that tuftsin requires two enzymes for its liberation from the parent carrier gamma-globulin. One enzyme is in the spleen that cleaves distal to the arginine end, and the other, on the outer side of the plasma membrane, cleaves proximal to the threonine residue. The tetrapeptide tuftsin stimulates all functions of phagocytic cells: phagocytosis, pinocytosis, motility, immunogenic activity including processing of the antigen and augmentation of the number of antibody-forming cells, bactericidal activity, and, above all, tumoricidal activity. The latter has been shown by several laboratories.

Overwhelming infection after splenectomy in spite of some spleen remaining and splenosis. A case report

A fatal case of overwhelming postsplenectomy pneumococcal sepsis is presented occurring in a 37-year-old female 11 years after removal of the spleen because of traumatic rupture. The patient died 11 h after admission to hospital and about 32 h after sudden onset of illness. At necropsy splenic tissue, splenosis, disseminated intravascular coagulation, and thrombi within the arterioles consisting of gram-positive cocci and adrenal hemorrhage were found. The clinical, laboratory, and postmortem findings are described. Reports had been published of 41 other cases of overwhelming postsplenectomy infection (OPSI) in patients aged 20 years or more, but only three of these cases of OPSI syndrome occurred in spite of remaining splenic tissue. The longest interval between extirpation of spleen and subsequent sepsis was 42 years, indicating a small but lifelong risk of severe infection in asplenic patients. In view of the literature, the role of spleen in infection defence, the splenic function in blood clearance, and the prevention of postsplenectomy infections by antibiotic prophylaxis, pneumococcal vaccine, and reimplantation of autochthonous splenic tissue or infrared contact coagulation are discussed.

Increased susceptibility of hypersplenic rats to infection with pneumococci

Hypersplenism was induced in rats by intra-peritoneal injections of methylcellulose. These rats developed an outsize spleen and had significantly depressed values for hemoglobin concentration, hematocrit and platelet count. The rats given methylcellulose were also found to be more susceptible to a challenge with a standardized intravenous injection of Streptococcus pneumoniae and had a significantly higher mortality rate than the control rats.

Monocyte cytotoxicity after splenectomy

Antibody-dependent cell-mediated cytotoxicity (ADCC) by monocytes was determined in 45 adults approximately 4 years after splenectomy for either abdominal trauma or accidental injury during operation for benign gastroduodenal ulcer. Compared to controls, both groups of splenectomized persons showed increased numbers of monocytes and decreased monocyte ADCC. The decrease of monocyte ADCC was only significant in those splenectomized persons in whom accessory splenic tissue was not detectable by isotope scanning. Addition of the spleen-dependent peptide tuftsin to monocytes in vitro did not augment their ADCC. An increase serum concentration of immune complexes was neither related to the presence of splenic tissue nor to the monocyte cytotoxicity. Vaccination with pneumococcal polysaccharide had no effect on monocyte ADCC. It is suggested that the defective monocyte cytotoxicity observed in splenectomized persons without detectable splenic tissue might be relevant to post splenectomy infectious susceptibility.

13C nuclear magnetic resonance and circular dichroism studies of the tuftsin conformation in water

13C-NMR and circular dichroic (CD) spectra of tuftsin and its analogues are discussed in connection with our hypothesis that the beta-turn is the biologically active conformation of tuftsin. The changes in CD spectra evoked by an increase in pH are interpreted as a demonstration of the increasing amount of beta-turn conformers in solution. Configurational changes in successive residues of tuftsin showed that residues 2 and 3 of the peptide chain are important for the tuftsin conformation.