Gonococcal infection in a nonhuman host is determined by human complement C1q

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Role of collectins and complement protein C1q in pregnancy and parturition

Collectins such as surfactant proteins SP-A, SP-D, and mannan-binding lectin (MBL), as well as complement protein C1q are evolutionarily conserved innate immune molecules. They are known to opsonize a range of microbial pathogens (bacteria, fungi, virus, and parasites) and trigger effector clearance mechanisms involving phagocytosis and/or complement activation. Collectins and C1q have also attracted attention in studies involving pregnancy as they are expressed in the female reproductive tissues during pregnancy; a unique state of immune suppression with increased susceptibility to infectious diseases. Recent studies are beginning to unravel their functional significance in implantation, placentation, pregnancy maintenance and parturition in normal and adverse pregnancies. Collectins and C1q, expressed in gestational tissues during pregnancy, might alter the status of mother's immune response to the allogenic fetus and the microenvironment, thereby serving as important regulators of fetus-mother interaction. Here, we discuss the functional roles that have been assigned to SP-A, SP-D, MBL and C1q in pregnancy and parturition.

Emerging and Novel Functions of Complement Protein C1q

Complement protein C1q, the recognition molecule of the classical pathway, performs a diverse range of complement and non-complement functions. It can bind various ligands derived from self, non-self, and altered self and modulate the functions of immune and non-immune cells including dendritic cells and microglia. C1q involvement in the clearance of apoptotic cells and subsequent B cell tolerance is more established now. Recent evidence appears to suggest that C1q plays an important role in pregnancy where its deficiency and dysregulation can have adverse effects, leading to preeclampsia, missed abortion, miscarriage or spontaneous loss, and various infections. C1q is also produced locally in the central nervous system, and has a protective role against pathogens and possible inflammatory functions while interacting with aggregated proteins leading to neurodegenerative diseases. C1q role in synaptic pruning, and thus CNS development, its anti-cancer effects as an immune surveillance molecule, and possibly in aging are currently areas of extensive research.

The sac-4 gene of Neisseria gonorrhoeae and co-existing chlamydial infection

BACKGROUND/OBJECTIVES

Recently, the sac-4 gene in Neisseria gonorrhoeae was postulated to increase the risk of developing mixed gonococcal and chlamydial infection. The aims of this study were to determine the frequency of the sac-4 gene in a larger sample of isolates of different serovars and to assess the prevalence of sac-4 in gonococcal isolates from patients with and without coexisting chlamydial infection.

METHODS

Isolates from 259 episodes of gonorrhoea were tested by a PCR assay for the sac-4 gene. The presence of co-existing chlamydial infection was determined from both laboratory and GUM clinical records.

RESULTS

The overall prevalence of sac-4 was 57.5% (149/259). The prevalence was not the same in all serovars and ranged from 34.9% in serovar 1B2 to 100% in serovar 1B18. Exact logistic regression analysis indicated significant differences in sac-4 prevalence in isolates of different serovars. The prevalence of sac-4 was 69.5% (41/59) in gonococcal isolates from patients with co-existing chlamydial infection compared with 57.9% (62/107) for those without chlamydial infection. Exact logistic regression analysis showed that the slightly increased sac-4 prevalence among chlamydia positive patients (p = 0.2) virtually disappeared when serovar status was taken into account (p > 0.9).

CONCLUSION

The sac-4 gene of the gonococcus does not increase the risk for mixed chlamydial infection.

Experimental gonococcal genital tract infection and opacity protein expression in estradiol-treated mice

The development of effective prophylactic agents against gonorrhea and the study of adaptation by Neisseria gonorrhoeae to the urogenital mucosa are hindered by the lack of a well-established animal model of gonococcal genital tract infection. Here, a murine model of long-term gonococcal genital tract infection is described. Female BALB/c mice were treated with 17-beta-estradiol and inoculated intravaginally with wild-type gonococcal strain FA1090 or MS11. N. gonorrhoeae was recovered from vaginal swabs for an average of 12 to 13 days following inoculation with 10(6) CFU of either strain. Inflammation occurred in over 80% of infected mice, and diplococci were associated with epithelial cells and neutrophils in stained vaginal smears. Ascended infection occurred in 17 to 20% of mice inoculated with strain FA1090. An outbred mouse strain (SLC:ddY) previously reported to be naturally susceptible to N. gonorrhoeae was also tested; however, as with BALB/c mice, estradiol was required for prolonged infection. Although piliation was not maintained during experimental murine infection, 46 to 100% of vaginal isolates from four of eight BALB/c mice and three of four SLC:ddY mice expressed one or more opacity (Opa) proteins within 4 days after inoculation with an Opa-negative variant of strain FA1090. The observed selection for and/or induction of gonococcal Opa protein expression during murine infection appears to parallel events that occur during experimental urethritis in volunteers.

Experimental transmission of Neisseria gonorrhoeae from pregnant rat to fetus

Sprague-Dawley rats were infected on day 20 of pregnancy by intraperitoneal inoculation with Neisseria gonorrhoeae. Disseminated gonococcal infection (DGI) and pelvic inflammatory disease (PID) strains in the presence of C1q but not in the presence of bovine serum albumin (BSA) were able to spread from the pregnant rat to the fetus and resulted in fetal mortality. Transmission of DGI and PID strains that are serum resistant (ser(r)) and sac-4 positive but not of a local infection strain that is ser(s) and sac-4 negative was facilitated by the C1q-dependent mechanism. This study provides the first experimental model that may mimic the transmission of gonococcal infection from mother to the fetus during pregnancy.

Binding of complement subcomponent C1q to Streptococcus pyogenes: evidence for interactions with the M5 and FcRA76 proteins

Binding of C1q, the first component of the complement system, to some human pathogens has been earlier reported. In the present study, direct binding of C1q to group A streptococci (GAS) of various serotypes as well as some other Gram-positive and Gram-negative species was demonstrated. The interaction between C1q and GAS was investigated more in detail. In hot neutral extracts of a number of GAS strains two components of 64 and 52 kDa, respectively, bound C1q; alkaline and SDS extracts yielded the 52 kDa component as the main C1q-binding substance. Trypsin treatment of the SDS extracts of two GAS strains suggested the C1q-binding component(s) to be of protein nature. C1q-binding material purified from the SDS extract of an avirulent strain, type T27, was separated in 12% SDS-PAGE and probed in Western blot with human C1q and fibrinogen, conjugated to horse radish peroxidase (HRP) as well as rabbit IgG antibodies complexed to HRP (PAP system). The 52 kDa component was non-reactive with fibrinogen or rabbit IgG. However, C1q-binding components purified from the alkaline extracts of two M-positive strains revealed strong binding of either fibrinogen (type M5) or both fibrinogen and rabbit IgG (type M76); the molecular mass of these components. 55 kDa and 43-40 kDa, respectively, was in agreement with the reported molecular mass of the M5 and FcRA76 proteins. Our findings suggest that C1q may interact with GAS through certain M-family proteins as well as by a so far unidentified surface factor of protein nature occurring in most GAS strains. The involvement of M-family proteins, regarded as virulence factors of these organisms, may suggest the interaction of GAS with C1q as biologically important.

Binding of vitronectin to opa-expressing Neisseria gonorrhoeae mediates invasion of HeLa cells

Neisseria gonorrhoeae induces local infections in the human genitourinary tract and can disseminate to other organs to cause severe disease. Blood-derived factors present in the genital mucosa have been suggested to facilitate the spread of N. gonorrhoeae in disseminated gonococcal infections. Using gentamicin invasion assays and confocal microscopy, we observed a strong stimulatory effect of fetal calf serum (FCS) on the gonococcal invasion of HeLa cells. FCS-mediated invasion was dependent on the expression of the epithelial cell invasion-associated Opa protein (plasmid-encoded Opa50 or its chromosomal homolog Opa30), while N. gonorrhoeae expressing noninvasive Opa proteins (Opa(51-60)) or no Opa protein (Opa-) was not invasive even in the presence of FCS. Incubation of N. gonorrhoeae MS11 with biotinylated FCS revealed a 78-kDa protein as the prominent protein binding to Opa50- or Opa30-expressing gonococci. This protein was recognized by antibodies against vitronectin (VN) in Western blots. Purified human or bovine VN efficiently bound to Opa50-expressing gonococci, while binding to noninvasive Opa- or Opa52-expressing gonococci was significantly lower. Binding of VN was inhibited by heparin in a concentration-dependent manner, indicating that the heparin binding sites present in VN or Opa50 may play an essential role in this interaction. Based on gentamicin invasion assays and confocal microscopy studies, VN binding was associated with an increased invasion of Opa50- and Opa30-expressing gonococci into HeLa cells. The ability of VN to mediate entry into epithelial cells may constitute an important event in the pathogenesis of local as well as disseminated gonococcal infections.

Pelvic inflammatory disease isolates of Neisseria gonorrhoeae are distinguished by C1q-dependent virulence for newborn rats and by the sac-4 region

The virulence mechanism of Neisseria gonorrhoeae in pelvic inflammatory disease (PID) is not well understood, and an objective diagnostic method to identify patients with PID is lacking. We investigated the hypothesis that development of PID was associated with a C1q-dependent virulence property of gonococcal strains. Recent development of a C1q-dependent experimental model of gonococcal infection (S. Nowicki, M. Martens, and B. Nowicki, Infect. Immun. 63:4790-4794, 1995) created an opportunity to evaluate this hypothesis in vivo. Therefore, the virulence of 32 clinical isolates (18 PID isolates and 14 local infection [LI] isolates) was evaluated in experimental rat pups. A serum bactericidal assay was used to characterize a gonococcal serum-resistant (ser(r)) phenotype. PCR primers designed to amplify a suitable-size gonococcal sac-4 DNA fragment (unique for serum-resistant donor JC1) were used to evaluate the association of serum-resistant genotype sac-4 with two phenotypes: C1q-dependent virulence expressed in vivo and resistance to bactericidal activity of human serum expressed in vitro. Strains were also characterized by auxotyping and serotyping. Of 32 gonococcal strains, 15 (46.7%) caused C1q-dependent bacteremia in rat pups and were sac-4 positive and ser(r). However, of the 15 isolates, 13 (87%) represented strains associated with human PID and 2 (13%) were associated with LI. None of the strains that were completely serum-sensitive (ser(s)) and sac-4 negative produced C1q-dependent bacteremia in rat pups, suggesting that both ser(r) and sac-4 were required for infection. The serum-resistant recombinant recipient of sac-4 produced C1q-dependent bacteremia in the rat model similarly to the serum-resistant donor of sac-4; the serum-sensitive parent strain did not produce bacteremia. These data suggest that sac-4-mediated serum resistance conferred C1q-dependent virulence and is a unique characteristic associated with PID. These newly identified features may contribute to the understanding of the pathogenic mechanism of PID-associated strains and open perspectives for establishing novel diagnostic methods.