Studies on Gonococcus infection. IX. In vitro decreased assocation of pilated gonococci with mouse peritoneal macrophages

Macrophage-Neisseria gonorrhoeae Interactions: A Better Understanding of Pathogen Mechanisms of Immunomodulation

Neisseria gonorrhoeae is a significant health problem worldwide due to multi-drug resistance issues and absence of an effective vaccine. Patients infected with N. gonorrhoeae have not shown a better immune response in successive infections. This might be explained by the fact that N. gonorrhoeae possesses several mechanisms to evade the innate and adaptative immune responses at different levels. Macrophages are a key cellular component in the innate immune response against microorganisms. The current information suggests that gonococcus can hijack the host response by mechanisms that involve the control of macrophages activity. In this mini review, we intend to condense the recent knowledge on the macrophage–N. gonorrhoeae interactions with a focus on strategies developed by gonococcus to evade or to exploit immune response to establish a successful infection. Finally, we discuss the opportunities and challenges of therapeutics for controlling immune manipulation by N. gonorrhoeae.

Neisseria gonorrhoeae induces a tolerogenic phenotype in macrophages to modulate host immunity

Neisseria gonorrhoeae is the etiological agent of gonorrhoea, which is a sexually transmitted disease widespread throughout the world. N. gonorrhoeae does not improve immune response in patients with reinfection, suggesting that gonococcus displays several mechanisms to evade immune response and survive in the host. N. gonorrhoeae is able to suppress the protective immune response at different levels, such as B and T lymphocytes and dendritic cells. In this study, we determined whether N. gonorrhoeae directly conditions the phenotype of RAW 264.7 murine macrophage cell line and its response. We established that gonococcus was effectively phagocytosed by the RAW 264.7 cells and upregulates production of immunoregulatory cytokines (IL-10 and TGF-β1) but not the production of proinflammatory cytokine TNF-α, indicating that gonococcus induces a shift towards anti-inflammatory cytokine production. Moreover, N. gonorrhoeae did not induce significant upregulation of costimulatory CD86 and MHC class II molecules. We also showed that N. gonorrhoeae infected macrophage cell line fails to elicit proliferative CD4+ response. This implies that macrophage that can phagocytose gonococcus do not display proper antigen-presenting functions. These results indicate that N. gonorrhoeae induces a tolerogenic phenotype in antigen-presenting cells, which seems to be one of the mechanisms to induce evasion of immune response.

Gonococcal arthritis

Disseminated gonococcal infection is the most common systemic complication of acute gonorrhea and occurs in 0.5% to 3.0% of patients with untreated mucosal infection. It is also the most common cause of septic arthritis in patients less than 30 years of age. Fortunately, the incidence of gonorrhea is decreasing dramatically in the United States and Western Europe, although it is still high in developing countries. Increasing resistance to antibiotics requires continuous surveillance of antimicrobial susceptibilities to determine the efficacy of current therapeutic measures.

Differential response of human monocytes to Neisseria gonorrhoeae variants expressing pili and opacity proteins

Experiments in vitro suggest that Neisseria gonorrhoeae surface variation plays a key role in gonococcal pathogenesis by providing the appropriate bacterial phenotypes to go through different stages of the infection. Here we report on the effects of phase and antigen variation of two major gonococcal adhesins, pili and opacity (Opa) outer membrane proteins, on the interaction of the gonococci with human monocytes. Using a set of recombinants of gonococcus strain MS11 that each express 1 of 11 genetically defined Opa proteins or a defined type of pilus, we found that both Opa proteins and pili promote bacterial phagocytosis by monocytes in the absence of serum and that this feature largely depends on the type of protein that is expressed. One of the Opa proteins (Opa[50]) strongly promoted uptake by monocytes but had little effect on the interaction with polymorphonuclear leukocytes under the conditions employed. Similarly, the phagocytosis-promoting effect of the pili was much more pronounced in monocytes than in neutrophils (4-fold versus 22-fold stimulation of uptake, respectively). Only a subpopulation of both types of phagocytes actively ingested bacteria, as has been observed during natural infections. Measurements of luminol-enhanced chemiluminescence demonstrated that phagocytosis of opaque but not piliated gonococci was accompanied by an increase in oxygen-reactive metabolites. These findings demonstrate that the monocyte response towards gonococci is highly dependent on the bacterial phenotype and differs from the neutrophil response. This diversity in bacterial behavior towards various types of human phagocytic cells underlines the biological impact of gonococcal surface variation and may explain previous contradictory results on this subject.

Phagocytic killing of Neisseria gonorrhoeae by human monocytes

The ability of human monocytes to phagocytize and kill nonpiliated opaque (T3) and transparent (T4) gonococci was investigated in a tumbling tube suspension assay. A serum-sensitive strain, F62, and a serum-resistant strain, FA19, were studied. CFU remaining after incubation with monocytes were used to assess the extent of killing. The data show that 50% of T3 and T4 gonococci of both strains were killed by monocytes over a 2-h period. Serum was necessary for the killing of transparent gonococci of both strains as well as for FA19 T3. Concentrations of serum ranging from 0.5 to 10% were equally effective, and heat-labile components were required. Killing of F62 T3, however, occurred in the absence of serum. An increased ratio of bacteria to monocytes decreased the rate of killing. A 30-min preopsonization of gonococci in 10% serum resulted in an enhanced rate of killing. Monocytes were able to kill plate-grown, but not log-phase, organisms. Disruption of the monocytes by sonication to release internalized bacteria did not increase the number of viable organisms. The addition of 10 micrograms of cytochalasin B per ml completely inhibited the reduction in colony numbers over time. These data indicate that freshly isolated human monocytes are capable of phagocytizing and killing nonpiliated gonococci.

In vitro kinetics of phagocytosis and intracellular killing of gonococci by peritoneal macrophages from mice deficient in complement component 5

Unstimulated resident peritoneal macrophages were harvested from complement-sufficient (C5+) and complement-deficient (C5-) mice by peritoneal lavage and cultured for 14 h. Adherence to cover slips was determined, and the monolayer was infected with transparent T1 gonococci. At various times after infection, the macrophages were observed for both attachment and phagocytosis of the gonococci by scanning and transmission electron microscopy. this analysis indicated that C5+ macrophages were capable of immediate phagocytosis of gonococci, with maximal phagocytosis occurring by 60 to 90 min. In contrast, C5- macrophages had a greater lag time before initiation of phagocytosis; this event was started by 30 min and completed by 90 min. The intracellular gonococci which were phagocytized by either C5+ or C5- mice were completely killed after 30 min of incubation. It appears that C5- mice are at a disadvantage in the early kinetics of the phagocytosis of gonococci, but that this does not affect the ultimate intracellular destruction of gonococci.

The biology of the gonococcus

Gonorrhea has been known since antiquity. Today, this disease is the most commonly reported infectious disease in the U.S. The natural environment of the etiological agent, Neisseria gonorrhoeae, is man. In this host, the organism usually parasitizes mucosal surfaces populated by columnar epithelial cells. Under certain conditions, the gonococcus may disseminate or spread to adjacent organs. The gonococcus is well adapted to its environment and is a successful parasite. Until recently, gonococci were uniformly sensitive to penicilin. However, a plasmid encoding beta-lactamase has been identified in some isolates. Most strains exhibit specific requirements for various amino acids, vitamins, purines, and pyrimidines. Only glucose, pyruvate, and lactate are utilized as sources of energy. Glucose is dissimilated by a combination of the Entner-Doudoroff and pentose phosphate pathways. A tricarboxylic acid cycle is also present and active under certain conditions. Structurally, the cell envelope of the gonococcus resembles that of a typical Gram-negative bacterium. Gonococci are highly autolytic, especially in older cultures or after depletion of the energy source. Autolysis is not due solely to peptidoglycan hydrolysis, but appears to involve a destabilization of the outer membrane as well. Cell surface components such as pili, lipopolysaccharide, outer membrane proteins, and a capsule are associated with the virulence and pathogenicity of this organism.

Quantitative measurement of phagocytosis of Neisseria gonorrhoeae by mouse peritoneal macrophages

The simultaneous labeling of gonococci with [6-3H]uracil and of mouse peritoneal macrophages with L-[U-14C]leucine permits a quantitative assessment of the association of gonococci with macrophages under various experimental conditions. Colony-type T1 (piliated) gonococci associated more than T4 (nonpiliated) organisms at 4 degrees C, but at 37 degrees C the association of T4 gonococci with macrophages exceeded that for the T1 organisms. The association of T1 gonococci with macrophages could be enhanced as much as 70-fold by homologous rabbit antisera prepared against whole, formaldehyde-treated organisms. This immune enhancement represented primarily increased phagocytosis rather than surface attachment, as shown by its inhibition at 4 degrees C or with 2-deoxyglucose. The data further suggested that this enhanced phagocytosis was mediated via the Fc receptor for immunoglobulin G.

Scanning electron microscopical examination of gonococcal urethral exudate

The relationship of gonococci and phagocytes in gonococcal urethral exudate was examined using a scanning electron microscope. Several stages in the phagocytic process were evident. These included pseudopodias, microvilli, and simple attachment of gonococci to phagocytic surfaces. Epithelial cells, also a part of the exudate, were examined in this study. Parallels are drawn between this and other phagocytic systems. The technique provides excellent preservation of phagocyte-bacterial interrelationships and offers a means of investigating the nature of the resistance of Neisseria gonorrhoeae to phagocytosis.

Serum and secretory antibody responses to Neisseria gonorrhoeae in patients with gonococcal infections

The present study was conducted to characterize the nature and pattern of serum and secretory antibody responses to N. gonorrhoeae by haemagglutination inhibition, opsonization, and immunofluorescence techniques in male and female patients with different clinical manifestations of gonorrhoea. Most male patients with acute gonococcal infection developed serum IgG and, less frequently, IgM antibodies against pilated gonococci within 2 weeks of infection and these antibodies declined to normal levels 1 to 2 months after treatment. This response was not noticeably different from the responses developed in male patients with subacute infection and female patients with chronic infection. Immunological analyses of the seminal plasmas and cervical fluids from these patients showed that antibodies reactive with both pilated and non-pilated N. gonorrhoeae are present in some of the cases. A small percentage of male patients who recovered from subacute gonococcal infection but not from acute infection possessed low levels of IgG and, less frequently, IgA antibodies to gonococcal antigens in their seminal plasmas. In contrast, more than half of the females with gonorrhoea had IgG antigonococcal antibodies in the cervical fluid. However, a small number of samples also showed the presence of IgA and IgM antibodies. IgA antibody in most of these IgA-positive samples was of the secretory type. The presence of secretory IgA (SIgA) in secretions and the lack of correlation between the antibody titres in serum and in secretions of these patients suggest that infection with N. gonorrhoeae may independently stimulate both a systemic and a local humoral immune response.

Studies on Gonococcus infection. X. Pili and leukocyte association factor as mediators of interactions between gonococci and eukaryotic cells in vitro

Two independent gonococcal surface components, pili and leukocyte association factor, appear to mediate in vitro interactions of Neisseria gonorrhoeae with tissue culture cells and human peripheral blood leukocytes, respectively.