The experimental and clinical use of immune-modulating drugs in the prophylaxis and treatment of infections

Restoration of polymorphonuclear leukocyte function in elderly subjects by thymomodulin

Senescence is a specific physiological evolution of human beings associated with a reduction in the functionality of several apparatuses, including the immune system. Thymomodulin (TMD) contains thymus polypeptides (< 10,000 D) and it has been used in a variety of disorders associated with defective immunological functions. The aim of this study was to investigate the effect on polymorphonuclear leukocyte (PMNs) phagocytosis and oxidative burst of a 6-week treatment with 160 mg/day TMD orally in elderly subjects (85.5 +/- 9.7 years). Elderly subjects have impaired PMN phagocytosis and the following release of oxidant radicals. Treatment with TMD for 6 weeks had a restoring effect; phagocytosis and the phagocytic index were significantly improved, with increases of 132.6% and 112.5%. These findings indicate that TMD might be given to enhance the immunodefenses of immunocompromised elderly subjects. Luminol-dependent chemiluminescence was increased by 15.6%, which was not significant, indicating a different response between phagocytosis and release of oxidant radicals.

Roles of peripheral leukocytes and tissue macrophages in antibacterial resistance induced by free or liposome-encapsulated muramyl tripeptide phosphatidylethanolamide

Administration of free muramyl tripeptide phosphatidylethanolamide (MTPPE) or liposome-encapsulated MTPPE (LE-MTPPE) in a twofold-lower dose at 24 h before bacterial inoculation resulted in clearance of intravenously inoculated Klebsiella pneumoniae by tissue macrophages, whereas in control mice, bacteria were not effectively cleared from the blood. In addition, MTPPE and LE-MTPPE led to increased numbers of leukocytes in the blood, which could compensate for the leukopenia in mice resulting from infection with K. pneumoniae. In an attempt to elucidate the relative contributions of the activation of tissue macrophages and the recruitment of leukocytes to the antibacterial resistance induced by MTPPE and LE-MTPPE, mice were infected intraperitoneally with K. pneumoniae. In these MTPPE- and LE-MTPPE treated mice, intraperitoneal influx of leukocytes and the phagocytic capacity of leukocytes were not higher than in untreated control mice. However, MTPPE- and LE-MTPPE-treated mice survived much longer; eventually 33% of the LE-MTPPE-treated mice survived, whereas all untreated control mice died as a result of bacterial septicemia. This prevention of early death appeared to be the result of an increased clearance of bacteria from the blood by activated tissue macrophages. It was observed that depletion of these tissue macrophages in liver and spleen abrogates the effect of LE-MTPPE treatment, indicating that tissue macrophages are of major importance in the LE-MTPPE-induced resistance against K. pneumoniae infection.

Free versus liposome-encapsulated muramyl tripeptide phosphatidylethanolamide in treatment of experimental Klebsiella pneumoniae infection

The effect of free and liposome-encapsulated muramyl tripeptide phosphatidylethanolamide (MTPPE) on resistance to Klebsiella pneumoniae infection in mice was investigated. It was shown that administration of MTPPE, at 24 h before bacterial inoculation, led to a dose-dependent antibacterial resistance in terms of increased clearance of bacteria from the blood and bacterial killing in various organs. The lowest effective dose of MTPPE was 50 micrograms per mouse. Administration of liposome-encapsulated MTPPE was also effective at a dose of 25 micrograms per mouse. The time of administration of both free and liposome-encapsulated MTPPE, with respect to the appearance of bacteria in the blood, was very important and indicated that repeated administration is necessary to obtain protection for a prolonged period. In view of the toxicity of MTPPE, it was an important observation that repeated administration of MTPPE in the liposome-encapsulated form also produced antibacterial resistance. Administration of free and liposome-encapsulated MTPPE resulted in increased numbers of granulocytes, monocytes, and lymphocytes in the blood of uninfected mice and prevented leukopenia in infected mice.

Steroidal glycolipid, L-644,257, is a potent enhancer of nonspecific host resistance

A steroidal glycolipid that enhances the nonspecific cellular response to opportunistic infection in an immunocompromised host has been discovered. A dose dependent response with 6-(5-cholesten-3 beta-yloxy)hexyl 1-thio-beta-D-mannopyranoside, L-644,257, was observed against several infective agents including bacterial, fungal, and viral pathogens in cyclophosphamide-treated mice. A mechanism for this protective action is proposed.

Effect of free or liposome-encapsulated muramyl dipeptide on uptake and intracellular survival of Listeria monocytogenes in mouse peritoneal macrophages in vitro

The effect of free versus liposome-encapsulated muramyl dipeptide (MDP) on the uptake and intracellular survival of Listeria monocytogenes in mouse peritoneal macrophages in vitro was investigated. Macrophages in monolayer culture were exposed to free MDP at various concentrations during different time periods before incubation with Listeria monocytogenes. An increase in bacterial uptake dependent on the concentration of MDP and the length of exposure was observed. Exposure of macrophages to 200 micrograms of free MDP per milliliter for 15 h led to a threefold increase in bacterial uptake, resulting in an average of 15 bacteria per macrophage after 30 min of incubation. In addition, intracellular bacteria were killed in the MDP-exposed macrophages, in contrast to the intracellular multiplication of Listeria monocytogenes in macrophages not exposed to MDP. Encapsulation of MDP within liposomes resulted in a significant enhancement of its activity: liposomal encapsulation led to a 1,000-fold reduction in the amount of MDP required to obtain these effects on bacterial uptake and intracellular killing, whereas empty liposomes had no effect at all. Liposomal encapsulation may be an appropriate means of increasing delivery of the muramyl peptides to the macrophages.

Thymomodulin: biological properties and clinical applications

Thymomodulin (Ellem Industria Farmaceutica s.p.a., Milan, Italy) is a calf thymus acid lysate derivative, composed of several peptides with a molecular weight range of 1-10 kD. Thymomodulin did not exhibit any mutagenic effect. Furthermore, thymomodulin used in animal studies showed no toxicity even when used at high concentrations. Of major significance are the observations in murine and human systems that thymomodulin remains active when administered orally. In vitro and in vivo administered thymomodulin was able to induce the maturation of T-lymphocytes. Additionally, studies in vitro showed that this thymic derivative can enhance the functions of mature T-lymphocytes with cascading effects on B-cell and macrophage functions. Extensive human clinical trials with thymomodulin showed that this agent can improve the clinical symptoms observed with various disease processes, including infections, allergies and malignancies, and can improve immunological functions during ageing.

Update on antibiotics in ocular infections

Each year, new antimicrobials are found or synthesized in an effort to improve the chance of overcoming infections. In the early 1950s, the only antibiotic available for ocular use was penicillin. Today, ophthalmologists can make a choice from a large selection of antibiotics for ocular infections. The majority of antibiotics have been literally unearthed, since worldwide soil surveys may have been the means of their discovery. In addition, synthetic derivatives of penicillin, cephalosporins, aminoglycosides, and tetracyclines, as well as drugs against tuberculosis and fungi, have become available, and new names have been added to the already bewildering list of less frequently used sulfonamides. However, it takes several years to appreciate the impact of new agents and the continued contribution of older ones. Constant reevaluation is mandatory. The real benefits as well as the untoward effects of a new antimicrobial agent may not be known until several years after the clinical introduction. In addition to approaching infection from the viewpoint of the offending organism and a specific antibiotic to address this organism, one may also approach this problem from the host's immunity. Until now, we have relied largely on the corticosteroids, but one must also consider various nonsteroidal anti-inflammatory agents and, even more importantly, the development of drugs to enhance the host's natural immunity.