Immunocompetent cells in resistance to bacterial infections

Tuberculosis: An Overview of the Immunogenic Response, Disease Progression, and Medicinal Chemistry Efforts in the Last Decade toward the Development of Potential Drugs for Extensively Drug-Resistant Tuberculosis Strains

Tuberculosis (TB) is a slow growing, potentially debilitating disease that has plagued humanity for centuries and has claimed numerous lives across the globe. Concerted efforts by researchers have culminated in the development of various strategies to combat this malady. This review aims to raise awareness of the rapidly increasing incidences of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis, highlighting the significant modifications that were introduced in the TB treatment regimen over the past decade. A description of the role of pathogen-host immune mechanisms together with strategies for prevention of the disease is discussed. The struggle to develop novel drug therapies has continued in an effort to reduce the treatment duration, improve patient compliance and outcomes, and circumvent TB resistance mechanisms. Herein, we give an overview of the extensive medicinal chemistry efforts made during the past decade toward the discovery of new chemotypes, which are potentially active against TB-resistant strains.

Genetic diversity of MHC-B in 12 chicken populations in Korea revealed by single-nucleotide polymorphisms

This study used a single-nucleotide polymorphism (SNP) panel to characterise the diversity in the major histocompatibility complex B region (MHC-B) in 12 chicken populations in Korea. Samples were genotyped for 96 MHC-B SNPs using an Illumina GoldenGate genotyping assay. The MHC-B SNP haplotypes were predicted using 58 informative SNPs and a coalescence-based Bayesian algorithm implemented by the PHASE program and a manual curation process. In total, 117 haplotypes, including 24 shared and 93 unique haplotypes, were identified. The unique haplotype numbers ranged from 0 in Rhode Island Red to 32 in the Korean native commercial chicken population 2 ("Hanhyup-3ho"). Population and haplotype principal component analysis (PCA) indicated no clear population structure based on the MHC haplotypes. Three haplotype clusters (A, B, C) segregated in these populations highlighted the relationship between the haplotypes in each cluster. The sequences from two clusters (B and C) overlapped, whereas the sequences from the third cluster (A) were very different. Overall, native breeds had high genetic diversity in the MHC-B region compared with the commercial breeds. This highlights their immune capabilities and genetic potential for resistance to many different pathogens.

Recombinant Salmonella typhimurium strains that invade nonphagocytic cells are resistant to recognition by antigen-specific cytotoxic T lymphocytes

To address the question of whether Salmonella-infected nonphagocytic cells could serve as target cells for recognition by antigen-specific, major histocompatibility complex class I-restricted cytotoxic T lymphocytes (CTL), four recombinant Salmonella typhimurium constructs that expressed full-length, or fragments of, influenza A virus nucleoprotein (NP) were made. The bacteria were shown to infect Chinese hamster ovary (CHO) cells. Appropriate major histocompatibility complex restriction molecules, HLA-B27 and H-2 Db, were transfected into CHO cells, which were then infected with recombinant S. typhimurium and used as targets for NP-specific CTL. The cells in which NP was expressed by intracellularly replicating bacteria were not lysed by NP-specific CTL, although they were killed when appropriate influenza A virus or peptides were used. Thus, S.typhimurium bacteria within nonphagocytic cells were resistant to CTL recognition. In contrast to these results, mice infected with recombinant S.typhimurium that expressed fragments of NP in the periplasm were primed for NP-specific CTL responses. The results indicate that CTL responses specific to Salmonella antigens can be generated, but the bacteria may be safe from the CTL attack once they have entered the nonphagocytic cells.

Oral administration of TNP-Lactobacillus conjugates in mice: a model for evaluation of mucosal and systemic immune responses and memory formation elicited by transformed lactobacilli

Safe live vector systems are being developed for oral delivery of antigens. A transformation system for indigenous Lactobacillus species of the gastrointestinal tract is described. Model systems were set up to evaluate immune responses. Orally administered trinitrophenylized (TNP) Lactobacillus were examined for their ability to induce immunological memory formation via determination of specific antibody titres in serum. We demonstrate a direct correlation between the level of systemic memory formation, as revealed by specific anti-TNP IgG serum antibodies, and the TNP substitution ratio of the Lactobacillus suspension used for oral priming. The specific IgG anti-TNP serum titres were comparable to or even higher than the titres of parental intraperitoneally primed animals. These results demonstrate the feasibility of using orally administered antigen-Lactobacillus as a future approach to vaccination.

Pathogenesis and immunity in murine salmonellosis

Salmonella is traditionally described as a facultative intracellular parasite, and host macrophages are regarded as the primary effector cells in both native and acquired immunity in mouse typhoid. This concept has not been unanimously accepted in the literature. Based on cell culture experiments and electron microscopic examinations of infected tissues, we observed that virulent Salmonella typhimurium is killed within polymorphs and macrophages of guinea pigs and mice. In a systemic disease, the organism propagates primarily in the extracellular locations of sinusoids and tissue lesions and within hepatocytes. Hence, it is more likely to be an extracellular pathogen and its virulence is directly related to its antiphagocytic property. The conspicuous absence of macrophages in the primary lesions of murine salmonellosis disputes the likelihood of their significant role in native resistance to the disease. Acquired cellular immunity is expressed as an enhanced antibacterial activity of macrophages facilitated by cytophilic antibodies rather than as an altered antibacterial action of immune macrophages. It is proposed that acquired immunity in murine salmonellosis is a synergistic manifestation of the innate capacity of polymorphs and macrophages to destroy ingested salmonellae, the activated antibacterial functions of macrophages mediated by cytophilic antibodies, the opsonic and agglutinating actions of antiserum, and the accelerated inflammation associated with delayed hypersensitivity to bacterial antigens. Unlike live attenuated vaccines, nonviable vaccines offer a significant, though not a solid, protection against subsequent challenges.

Deficient immune interferon production in tuberculosis

Production of interferon (IFN)-alpha and -gamma by peripheral blood mononuclear cells (PBMC) were studied in 28 patients with active tuberculosis and 28 healthy control subjects matched for age, sex, ethnic origin and diet. No significant differences were found between patients and matched controls in mean titres of IFN-alpha induced by Newcastle disease virus, IFN-gamma induced by staphylococcal enterotoxin A with tetrahydrophorbyl acetate, and IFN-gamma induced by purified protein derivative (PPD). However, a subset of nine out of 25 tuberculosis patients tested produced low titres (less than 100 u/ml) of IFN-gamma in response to PBMC stimulation with PPD. In comparison to other patients, this group was characterized by lower IFN-alpha and IFN-gamma responses to virus and mitogens respectively, relative anergy to tuberculin skin testing, depressed in vitro PBMC proliferative responses to PPD, and neutrophil leucocytosis. In all nine patients effective chemotherapy restored cutaneous reactivity, PBMC proliferative responses, neutrophil counts and IFN-alpha responses to virus by 6 months, and also IFN-gamma responses to PPD in one patient re-tested.

Lymphoblastoid cell supernatants increase expression of C3b receptors on human polymorphonuclear leucocytes: direct binding studies with 125I-C3b

Human PMN incubated in culture supernatants of the Raji long-term human lymphoblastoid cell line showed increased rosette formation with sheep erythrocytes coated with C3b (EIgM C4b3b) but no change in rosette formation with IgG-coated erythrocytes. This suggested a specific increase in cell surface C3b receptors, which was further investigated using 125I-C3b for direct binding studies. The results confirmed that specific binding of 125I-C3b to PMN incubated in culture supernatants increased up to three- to four-fold over binding to PMN incubated in control media alone. Scatchard analysis revealed that the apparent Ka for supernatant-treated cells, 3.36 +/- 0.89 X 10(7) L/M did not differ from the Ka for cells incubated in control media, 3.76 +/- 0.75 X 10(7) L/M, suggesting an increase in a single class of C3b receptors. Kinetic studies revealed that the active factor was present within 24 hr of culture of the Raji cells, and that neutrophils incubated in culture supernatants increased their C3b receptors continuously for up to 4 hr, the longest interval tested. The effect of the culture supernatant was lost with dilution beyond eight- to 10-fold. The results suggest that culture supernatants of this long-term lymphoblastoid cell line contain soluble factors that induce increased expression of C3b receptors on PMN and may thus serve as a model for study of important physiologic effects of lymphocyte products on PMN in vivo.

The suppressive effect of peritoneal exudate macrophages on production of antibody to sheep erythrocytes in vitro

The effects of peritoneal exudate macrophages on antibody response to sheep erythrocytes (SRBC) were investigated in mice. Peritoneal exudate macrophages obtained from mice injected intraperitoneally with proteose peptone or Corynebacterium parvum 4 days earlier had stronger ability to phagocytize and degrade SRBC than normal resident macrophages. These macrophages suppressed antibody formation to SRBC in vitro as well as in vivo. This suppression was overridden by increasing the amount of SRBC and diminished completely by pretreatment of the macrophages with iodoacetate and partly by pretreatment with 2-deoxyglucose, both known to be inhibitors of phagocytosis, but not by addition of indomethacin to the in vitro culture. These results suggest that the suppression of antibody response by peritoneal exudate macrophages was due to the increased activity of these cells as scavenger cells, resulting in a reduced amount of effective antigenic stimulation, and that it was not mediated by a prostaglandin-dependent mechanism. The scavenger function of these macrophages may be due to Ia-negative macrophages.

Development of immunity against Listeria monocytogenes in athymic nude versus neonatally thymectomized mice

The thymus requirement for the development of immunological responsiveness was determined by estimation of immune responses raised to Listeria monocytogenes in athymic nude, neonatally thymectomized, and sham-operated mice at 6 weeks of age. Not only sham-operated mice, but also neonatally thymectomized mice could completely eliminate the bacteria from the spleen and liver, while athymic nude mice could not eliminate them and showed a persistent form of infection. A strong delayed footpad reaction and acquired cellular resistance could be raised in neonatally thymectomized mice just as well as in sham-operated mice, but not in athymic nude mice. The delayed footpad reaction could be induced in neonatally thymectomized mice without an accompanying ability to inhibit macrophage migration. These results suggest that T cells responsible for immunity against listerial infection require the presence of the thymus for only a very short period in their development.

Two steps in the generation of acquired cellular resistance against Listeria monocytogenes: accumulation and activation of macrophages

Mice were immunized with 1 X 10(3) viable Listeria monocytogenes, and the mechanism of the acquired resistance against challenge infection with 5 X 10(4) L. monocytogenes was studied by the use of the peritoneal cavity of mice as the site of challenge. An enhanced elimination of bacteria from the peritoneal cavity became detectable on day 5 after immunization, and lasted thereafter. Before day 10 postimmunization, a marked accumulation of macrophages was observed after the challenge but the in vitro listericidal activity of macrophages was not so enhanced. After day 15 postimmunization, peritoneal macrophages did not increase in number after the challenge but the in vitro listericidal activity of macrophages was the stronger. Accumulation of non-activated macrophages seemed to contribute mainly to the expression of acquired resistance against challenge in the early stage of immunization. So-called activated macrophages appeared to be generated only in the later stage of immunization. Thus it was suggested that there may be at least two steps in the expression of acquired listerial resistance.

Salmonella typhimurium infection in calves: delayed specific skin reactions directed against the O-antigenic polysaccharide chain

Specific delayed skin reactions developed after intradermal injection of Salmonella typhimurium lipopolysaccharide in 12-week-old calves which had been orally infected with S. typhimurium 5 weeks earlier. Uninfected calves showed no delayed skin reactions. Skin biopsies from skin swellings showed a massive infiltration of mononuclear cells in the skin of infected calves but not in those of uninfected calves. Persistence of infection in infected calves was confirmed by isolation of S. typhimurium from fecal specimens. The delayed skin reactions could be shown to be specific and directed against the O-polysaccharide chain of the lipopolysaccharide since none of the lipopolysaccharide chain of the lipopolysaccharide since none of the lipopolysaccharide preparations from a rough mutant of S. typhimurium, two strains with different O-polysaccharide chains, or lipid A elicited skin reactivity. To cause a reaction, the O-polysaccharide had to be in a macromolecular complex, since skin swellings were seen only after injections of either O-polysaccharide chains cross-linked by 1,2,3,4-diepoxybutane or octasaccharides from the O chain covalently linked to a straight 12-carbon aliphatic chain forming an artificial glycolipid. Injection of the pure octasaccharides of O-polysaccharide chains failed to elicit delayed skin reactions.

Enhanced elimination of Listeria monocytogenes at the site of delayed footpad reaction

The protective activity against a challenge infection with Listeria monocytogenes was investigated at the site of a delayed footpad reaction in mice immunized with viable or killed listeria. Delayed footpad reactivity was induced only in mice immunized with viable bacteria. Rapid and marked elimination of challenge bacteria was observed only at the site of reaction in mice immunized with viable bacteria but not in mice immunized with killed bacteria. Macrophage migration inhibitory activity was observed equally in both groups of mice. These results suggest that the delayed footpad reaction contributes directly to the elimination of bacteria irrespective of macrophage migration inhibitory activity.

Delayed hypersensitivity to Staphylococcus aureus in mice: in vitro responses to isolated Staphylococcal antigens

Isolated Staphylococcal cellular components were used to evaluate the in vitro reactivity of lymphocytes from mice with delayed hypersensitivity to Staphylococcus aureus. Macrophage migration inhibition studies showed that splenic lymphocytes from mice sensitized with three injections of S. aureus inhibited macrophage migration when stimulated with S. aureus sonicate antigen (SASA), cell membrane (CM), and purified membrane protein (PMP). Continued injections (seven) resulted in migration inhibition when the sensitized cells were reacted with SASA, CM, PMP, cell wall (CW), and protein A (PA). Lymphocyte stimulation studies following three injections further illustrated the role of membrane proteins in the early phase of mouse reactivity. Splenic lymphocytes were maximally stimulated by SASA, CM, and PMP. Lipoteichoic acid (LTA), teichoic acid (TA), and CW also were stimulatory but to a much lesser degree. Mice receiving seven S. aureus injections had a high basal stimulatory response which overshadowed the responses to the isolated staphylococcal components. All of the staphylococcal components except LTA were mitogenic for splenic B lymphocytes. The mitogenicity was dependent upon the presence of macrophages. Only SASA, CM, and PMP were mitogenic for non-enriched splenic lymphocytes.

Adjuvanticity of lactobacilli. I. Differential effects of viable and killed bacteria

The adjuvanticity of Lactobacillus brevis and Lactobacillus plantarum was the subject of this study. The latter was the better adjuvant in both delayed hypersensivity and antibody formation to sheep red blood cells. Viable L. plantarum stimulated exclusively the delayed hypersensivity, where heat-killed bacteria had an adjuvant effect on antibody formation. For optimal adjuvant effects lactobacilli had to be injected in a dose of 10(8) into the same site as the antigen. Viable lactobacilli and to a lesser degree heat-killed bacteria induce hepato-splenomegaly, suggesting mediation of the adjuvant activity by the reticuloendothelial system. Granuloma formation with mainly mononuclear cell infiltrates could be observed after subcutaneous administration of viable lactobacilli whereas heat-killed lactobacilli induced granulomata containing about equal numbers of granulocytes and mononuclear cells. The possible clinical application of L. plantarium in the immunotherapy of tumours is suggested.

Stimulation of polymorphonuclear leukocyte bactericidal activity by supernatants of activated human mononuclear cells

Supernatants of phytohemagglutinin-activated human mononuclear cells stimulated polymorphonuclear leukocyte (PMN) activity against the gram-negative organism Serratia marcescens. In the absence of serum opsonins, when control PMN could not impede bacterial growth, stimulated PMN averaged more than 0.6-log kill of the original bacterial inoculum. In the presence of optimal amounts of serum opsonins, when control PMN were significantly bactericidal, stimulated PMN killed, on the average, at least 0.6 log more of bacteria. Stimulation was not found when PMN were preincubated with supernatants for 1 h or less. The data strongly suggested that the action of the PMN stimulating factor was independent of and different from classically described serum opsonins. PMN stimulating activity may be an additional lymphokine-mediated immune defense mechanism enabling hosts to kill invading microorganisms.

Mediation of immunity to intracellular infection (Toxoplasma and Besnoitia) within somatic cells

Antigen-treated lymphocytes from immune hamsters specifically protected not only macrophages, but also cultured fibroblasts and kidney cells infected with Toxoplasma gondii or Besnoitia jellisoni. Macrophages were not necessary for the protection of fibroblasts and kidney cells. A mediator that inhibited the intracellular proliferation of these microbes was obtained from immune lymphocytes in contact with specific antigen. Again, macrophages were not necessary for the elaboration of this mediator or its activity in kidney cells or fibroblasts. The mediator was microbe and host specific, had a molecular weight between 4,000 and 5,000, was resistant to heating at 56 degrees C for 30 min, and was sensitive to chymotrypsin, but resistant to ribonuclease and deoxyribonuclease. A single injection of Besnoitia mediator afforded better protection to hamsters infected with Besnoitia than did antibody. Whereas antibody lysed extracellular organisms, the microbe-specific mediators conferred immunity not only on macrophages, but also on other cells of the body, apparently the first such demonstration.

In vitro guinea pig leukocyte reactions to Rickettsia rickettsii

The presence of cell-mediated immunity in Rocky Mountain spotted fever-infected guinea pigs was determined by two in vitro assays: whole blood lymphocyte transformation (LT) and macrophage migration inhibition. Increased LT was detected as early as 1 week in guinea pigs infected with Rickettsia rickettsii and treated with oxytetracycline and was detected by two weeks in infected but untreated guinea pigs. Elevated LT was still detectable at 10 weeks postinfection. Guinea pigs vaccinated with killed rickettsiae failed to develop lymphocyte responsiveness; however, there was a rapid lymphocyte response after challenge with live organisms, suggesting potentiation by the vaccine. Vaccinated guinea pigs that were challenged and then treated with antibiotic failed to develop LT, suggesting that infection is necessary for the observed response. Macrophage migration inhibition was detected in both infected and vaccinated guinea pigs by 1 week after infection, but this response was no longer detected 4 to 5 weeks later. Antibody appeared at 2 to 3 weeks postinfection and was present at low levels through week 10. Antibody-treated rickettsiae were phagocytized and destroyed by guinea pig peritoneal macrophages, whereas normal serum-treated rickettsiae replicated and eventually destroyed the phagocytes.

Interactions between salmonellae and macrophages of guinea pigs. IV. Relationship between migration inhibition and antibacterial action of macrophages

The in vitro macrophage migration inhibition test was used to detect the development of delayed-type hypersensitivity in guinea pigs infected with Salmonella typhimurium. Four different preparations from supernatants of S. typhimurium cultures were used as the antigens in this test. They included the concentrated bacterial antigens, the high-molecular-weight (>50,000) antigens, the ammonium sulfate-precipitated antigens, and the ribonuclease-treated antigens. All four antigen preparations were shown to inhibit the migration of peritoneal macrophages of salmonella-infected (immune) guinea pigs from capillary tubes, in comparison with cells of normal control animals. By use of the high-molecular-weight antigens and the ammonium sulfate-precipitated antigens, the production of the migration inhibition factor(s) was elicited from cultures of lymphocytes obtained from the peripheral blood of immune guinea pigs. The activity of the migration inhibition factor(s) was demonstrated by its ability to inhibit the migration of peritoneal macrophages of normal guinea pigs from capillary tubes. In contrast, normal peritoneal macrophages exposed to products of antigen-stimulated immune lymphocytes did not exhibit an enhanced phagocytic or bactericidal action against virulent S. typhimurium as compared with those of the normal control. The present study indicated that the bacterial antigens responsible for the elicitation of the production of the migration inhibition factor from lymphocytes of immune guinea pigs are inactivated by proteolytic enzymes, but not by ribonuclease, and have molecular weights of >50,000.