The role of complement in host resistance to bacteria

In vitro evaluation of complement deposition and opsonophagocytic killing of Rhodococcus equi mediated by poly-N-acetyl glucosamine hyperimmune plasma compared to commercial plasma products

Background

The bacterium Rhodococcus equi can cause severe pneumonia in foals. The absence of a licensed vaccine and limited effectiveness of commercial R. equi hyperimmune plasma (RE‐HIP) create a great need for improved prevention of this disease.

Hypothesis

Plasma hyperimmune to the capsular polysaccharide poly‐N‐acetyl glucosamine (PNAG) would be significantly more effective than RE‐HIP at mediating complement deposition and opsonophagocytic killing (OPK) of R. equi.

Animals

Venipuncture was performed on 9 Quarter Horses.

Methods

The ability of the following plasma sources to mediate complement component 1 (C1) deposition onto either PNAG or R. equi was determined by ELISA: (1) PNAG hyperimmune plasma (PNAG‐HIP), (2) RE‐HIP, and (3) standard non‐hyperimmune commercial plasma (SP). For OPK, each plasma type was combined with R. equi, equine complement, and neutrophils isolated from horses (n = 9); after 4 hours, the number of R. equi in each well was determined by quantitative culture. Data were analyzed using linear mixed‐effects regression with significance set at P < .05.

Results

The PNAG‐HIP and RE‐HIP were able to deposit significantly (P < .05) more complement onto their respective targets than the other plasmas. The mean proportional survival of R. equi opsonized with PNAG‐HIP was significantly (P < .05) less (14.7%) than that for SP (51.1%) or RE‐HIP (42.2%).

Conclusions and Clinical Importance

Plasma hyperimmune to PNAG is superior to RE‐HIP for opsonizing and killing R. equi in vitro. Comparison of these 2 plasmas in field trials is warranted because of the reported incomplete effectiveness of RE‐HIP.

Increased severity of respiratory infections associated with elevated anti-LPS IgG2 which inhibits serum bactericidal killing

An antibody directed against the O-antigen of Pseudomonas aeruginosa LPS can block complement-mediated bacterial killing and contributes to the severity of respiratory infection.

Although specific antibody induced by pathogens or vaccines is a key component of protection against infectious threats, some viruses, such as dengue, induce antibody that enhances the development of infection. In contrast, antibody-dependent enhancement of bacterial infection is largely unrecognized. Here, we demonstrate that in a significant portion of patients with bronchiectasis and Pseudomonas aeruginosa lung infection, antibody can protect the bacterium from complement-mediated killing. Strains that resist antibody-induced, complement-mediated killing produce lipopolysaccharide containing O-antigen. The inhibition of antibody-mediated killing is caused by excess production of O-antigen–specific IgG2 antibodies. Depletion of IgG2 to O-antigen restores the ability of sera to kill strains with long-chain O-antigen. Patients with impaired serum-mediated killing of P. aeruginosa by IgG2 have poorer respiratory function than infected patients who do not produce inhibitory antibody. We suggest that excessive binding of IgG2 to O-antigen shields the bacterium from other antibodies that can induce complement-mediated killing of bacteria. As there is significant sharing of O-antigen structure between different Gram-negative bacteria, this IgG2-mediated impairment of killing may operate in other Gram-negative infections. These findings have marked implications for our understanding of protection generated by natural infection and for the design of vaccines, which should avoid inducing such blocking antibodies.

Photonic biosensor assays to detect and distinguish subspecies of Francisella tularensis

The application of photonic biosensor assays to diagnose the category-A select agent Francisella tularensis was investigated. Both interferometric and long period fiber grating sensing structures were successfully demonstrated; both these sensors are capable of detecting the optical changes induced by either immunological binding or DNA hybridization. Detection was made possible by the attachment of DNA probes or immunoglobulins (IgG) directly to the fiber surface via layer-by-layer electrostatic self-assembly. An optical fiber biosensor was tested using a standard transmission mode long period fiber grating of length 15 mm and period 260 μm, and coated with the IgG fraction of antiserum to F. tularensis. The IgG was deposited onto the optical fiber surface in a nanostructured film, and the resulting refractive index change was measured using spectroscopic ellipsometry. The presence of F. tularensis was detected from the decrease of peak wavelength caused by binding of specific antigen. Detection and differentiation of F. tularensis subspecies tularensis (type A strain TI0902) and subspecies holarctica (type B strain LVS) was further accomplished using a single-mode multi-cavity fiber Fabry-Perot interferometric sensor. These sensors were prepared by depositing seven polymer bilayers onto the fiber tip followed by attaching one of two DNA probes: (a) a 101-bp probe from the yhhW gene unique to type-A strains, or (b) a 117-bp probe of the lpnA gene, common to both type-A and type-B strains. The yhhW probe was reactive with the type-A, but not the type-B strain. Probe lpnA was reactive with both type-A and type-B strains. Nanogram quantities of the target DNA could be detected, highlighting the sensitivity of this method for DNA detection without the use of PCR. The DNA probe reacted with 100% homologous target DNA, but did not react with sequences containing 2-bp mismatches, indicating the high specificity of the assay. These assays will fill an important void that exists for rapid, culture-free, and field-compatible diagnosis of F. tularensis.

Pseudomonas aeruginosa lipopolysaccharide: a major virulence factor, initiator of inflammation and target for effective immunity

Pseudomonas aeruginosa is one of the most important bacterial pathogens encountered by immunocompromised hosts and patients with cystic fibrosis (CF), and the lipopolysaccharide (LPS) elaborated by this organism is a key factor in virulence as well as both innate and acquired host responses to infection. The molecule has a fair degree of heterogeneity in its lipid A and O-antigen structure, and elaborates two different outer-core glycoforms, of which only one is ligated to the O-antigen. A close relatedness between the chemical structures and genes encoding biosynthetic enzymes has been established, with 11 major O-antigen groups identified. The lipid A can be variably penta-, hexa- or hepta-acylated, and these isoforms have differing potencies when activating host innate immunity via binding to Toll-like receptor 4 (TLR4). The O-antigen is a major target for protective immunity as evidenced by numerous animal studies, but attempts, to date, to produce a human vaccine targeting these epitopes have not been successful. Newer strategies employing live attenuated P. aeruginosa, or heterologous attenuated bacteria expressing P. aeruginosa O-antigens are potential means to solve some of the existing problems related to making a P. aeruginosa LPS-specific vaccine. Overall, there is now a large amount of information available about the genes and enzymes needed to produce the P. aeruginosa LPS, detailed chemical structures have been determined for the major O-antigens, and significant biologic and immunologic studies have been conducted to define the role of this molecule in virulence and immunity to P. aeruginosa infection.

Helicobacter pylori eradication decreases the expression of glycosylphosphatidylinositol-anchored complement regulators, decay-accelerating factor and homologous restriction factor 20, in human gastric epithelium

BACKGROUND

It has previously been reported that there is a strong correlation between the expression of glycosylphosphatidylinositol (GPI)-anchored complement membrane inhibitor in gastric epithelium and the severity of inflammation of gastric mucosa. To investigate the regulation of complement activity in gastric epithelium during Helicobacter pylori (H. pylori)-associated gastritis, the expression of GPI-anchored complement membrane inhibitors, decay-accelerating factor (DAF) and 20-kDa homologous restriction factor 20 (HRF20), and membrane cofactor protein (MCP), which is a transmembrane protein, were evaluated after removal of the H. pylori stimulus. Furthermore, the expression of the complement fragment, C3c, was also investigated.

METHODS

Forty-six patients with epigastric symptoms and endoscopically confirmed peptic ulcer or gastritis who had H. pylori infection of the gastric mucosa were enrolled in the present study. Biopsy specimens were obtained from the gastric antrum and corpus 1 month before and after eradication. Helicobacter pylori infection was determined by the rapid urease test, histology, and culture before eradication, and by histology, culture, and urea breath test after eradication. Gastric biopsy specimens obtained before and after eradication were evaluated for infiltration by neutrophils and mononuclear cells. The expression of complement membrane inhibitors, DAF, HRF20, and MCP and that of the main complement fragment, C3c, was immunohistochemically evaluated.

RESULTS

One month after the eradication of H. pylori, the infiltration by neutrophils and mononuclear cells in the gastric mucosa decreased significantly (P < 0.0001) as compared with that before eradication. The expression of DAF, HRF20, and C3c on gastric mucosal epithelium also significantly decreased in both the antrum and the corpus (P < 0.05) 1 month after eradication. However, no change was observed in the expression of MCP.

CONCLUSIONS

The decrease in the expression of GPI-anchored complement regulator and the complement after removal of a chronic microbial stimulus suggests that the gastric epithelium appears to undergo an aggressive stress of complement during H. pylori infection. Conclusively, DAF and HRF20 may play an important protective role against complement-mediated damage induced by chronic microbial stimuli in such a pathological condition.

Protection mediated by antibodies to iron-regulated outer-membrane proteins of S. typhi in a mouse peritonitis model

Iron limitation induces the expression of iron-regulated outer-membrane proteins, which are not expressed under iron sufficient growth conditions. In the present study, these proteins were purified in order to evaluate their protective potential in the experimental model. Anti IROMPs antiserum was raised in rabbits. In mice, passively transferred anti-IROMPs antibodies provided 60% protection against the serovar Typhi challenge dose (9.6 LD50). The hyperimmune serum containing anti-IROMPs antibodies were also found to be bactericidal in the presence of complement whereas no bacterial killing was observed with pre-immunized serum. Bactericidal titre of anti-IROMPs serum was fond to be 2000 as more than 50% killing was observed with serum diluted to 1:2000. The role of IROMPs was assessed in actively-immunized mice followed by challenge with serovar Typhi. These proteins provided protection in 90% mice against challenge (480 LD50) with the pathogen. The levels of isotypes of antibodies (IgG, IgM & IgA) in the sera and secretory antibodies (sIgA) in the gut fluid of immunized mice correlated with the protection. This study, thus indicates that anti IROMPs antibodies may play an important role in providing protection at systemic as well as at mucosal level.

Herpes simplex virus 1 infected neuronal and skin cells differ in their susceptibility to complement attack

Herpes simplex virus type 1 (HSV-1) infection in neurons is lifelong and generally asymptomatic. Reactivation of this latent infection results in skin blistering whereas the respective peripheral neurons are rarely affected. Why the neuronal cells are spared while the skin cells are sacrificed is not well understood. In the present study our aim was to study whether neuronal and skin cells differ in their ability to control complement attack during HSV-1 infection. Human embryonal skin (HES) cells and neuronal Paju cells were infected by HSV-1 in vitro. Both types of infected cells activated complement but were initially resistant to membrane attack complex (MAC) deposition. During the first hours of infection the expression of the endogenous complement regulators decay accelerating factor (DAF) and CD59 increased on both HES and Paju cells. By 12 hr the infected HES cells had lost their ability to control complement attack. The expression of DAF and CD59 decreased and the cells became targets for MAC attack. In contrast, complement regulator expression on the Paju cells did not decrease below the initial level and complement C5b-9 deposition was found only on 10% of the Paju cells at 12 hr. The results suggest that HSV-infected neuronal cells are better than skin cells in protecting themselves against complement attack. This may contribute to the persistence of a latent HSV-1 infection in neuronal cells for prolonged periods.

Moraxella catarrhalis: from emerging to established pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.

Survival of Helicobacter pylori From complement lysis by binding of GPI-anchored protectin (CD59)

BACKGROUND & AIMS

Although Helicobacter pylori is sensitive to complement lysis in vitro, chronic infection persists for years. We tested whether H. pylori acquires complement resistance by binding glycolipid-tailed inhibitors from the host.

METHODS

Gastric biopsy specimens from H. pylori-infected patients (n = 10) and noninfected controls (n = 6) were analyzed for complement deposition and expression of the complement regulators protectin (CD59) and DAF. Protectin binding and complement sensitivity analyses were performed with the NCTC strain 11637 (CagA(+)) and 2 clinical isolates 9:0 (CagA(+)) and 67:20 (CagA(-)).

RESULTS

In the noninfected mucosa, protectin was strongly expressed on the membranes of epithelial cells, but in the infected epithelia the expression was granular and more focused to the mucus. H. pylori bacteria in the gastric pits were often positive for protectin but negative for C5b-9. An opposite pattern was seen on the surface mucosa. In vitro analyses using (125)I-CD59 and bacteriolysis assays showed that protectin bound to H. pylori and protected CagA(+) strains against complement killing. In an enzyme-linked immunosorbent assay, the binding of CD59 correlated inversely with the appearance of the C5b-9 neoantigen.

CONCLUSIONS

Binding of protectin inhibits membrane attack complex assembly on H. pylori and may thereby contribute to their survival on the gastric mucosa.

Milk immunoglobulins and complement factors

The importance of colostrum for the growth and health of newborn offspring is well known. In bovine colostrum, the antibody (immunoglobulin) complement system provides a major antimicrobial effect against a wide range of microbes and confers passive immunity until the calf's own immune system has matured. Bovine serum and lacteal secretions contain three major classes of immunoglobulins: IgG, IgM and IgA. The immunoglobulins are selectively transported from the serum into the mammary gland, as a result of which the first colostrum contains very high concentrations of immunoglobulins (40-200 mg/ml). IgG1 accounts for over 75 % of the immunoglobulins in colostral whey, followed by IgM, IgA and IgG2. All these immunoglobulins decrease within a few days to a total immunoglobulin concentration of 0.7-1.0 mg/ml, with IgG1 representing the major Ig class in milk throughout the lactation period. Together with the antibodies absorbed from colostrum after birth, the complement system plays a crucial role in the passive immunisation of the newborn calf. The occurrence of haemolytic or bactericidal complement activity in bovine colostrum and milk has been demonstrated in several studies. This review deals with the characteristics of bovine Igs and the complement system to be exploited as potential ingredients for health-promoting functional foods.

Complement-resistance mechanisms of bacteria

Despite more than a century of parallel research on bacteria and the complement system, relatively little is known of the mechanisms whereby pathogenic bacteria can escape complement-related opsonophagocytosis and direct killing. It is likely that pathogenicity in bacteria has arisen more accidentally than in viruses, and on the basis of selection from natural mutants rather than by outright stealing or copying of genetic codes from the host. In this review we will discuss complement resistance as one of the features that makes a bacterium a pathogen.

Acquired resistance of Escherichia coli to complement lysis by binding of glycophosphoinositol-anchored protectin (CD59)

Protectin (CD59) is a glycophosphoinsitol (GPI)-anchored defender of human cells against lysis by the membrane attack complex of complement. In this study, we examined whether protectin released from human cell membranes can incorporate into the surface of gram-negative bacteria. Analysis by using radiolabeled protectin, immunofluorescence, flow cytometry, and whole-cell enzyme-linked immunosorbent assay demonstrated that protectin bound to nonencapsulated Escherichia coli EH237 (Re) and EH234 (Ra) in a calcium-dependent manner. The incorporation required the GPI-phospholipid moiety since no binding of a phospholipid-free soluble form of protectin was observed. Mg2+ did not enhance the binding, and a polysialic acid capsule prevented it (strain IH3080 [O18:K1:H8]). Bound protectin inhibited the C5b-9 neoantigen expression on complement-treated bacteria. Protection against complement lysis was observed in both a colony counting assay and a bioluminescence assay, where viable EH234 bacteria expressing the luciferase gene emitted green light in the presence of the luciferine substrate. In general, two- to four-times-higher serum concentrations were needed to obtain 50% lysis of protectin-coated versus noncoated bacteria. The results indicate that protectin can incorporate in a functionally active form into the cell membranes of the two nonencapsulated deep rough E. coli strains studied.

Biologic activities of antibodies to the neutral-polysaccharide component of the Pseudomonas aeruginosa lipopolysaccharide are blocked by O side chains and mucoid exopolysaccharide (alginate)

Virulent strains of Pseudomonas aeruginosa are either of a nonmucoid, lipopolysaccharide (LPS)-smooth or mucoid, LPS-rough phenotype, and immunity to these different variants is efficiently mediated by antibodies specific to O antigens or mucoid exopolysaccharide (also called alginate), respectively. In addition to O side chains and core polysaccharide components, the LPS of P. aeruginosa also contains neutral-polysaccharide components that express antigenic determinants common to many clinical isolates. We evaluated antibodies specific to neutral polysaccharides for the ability to mediate opsonic killing and protective immunity. Antibodies to these antigens mediated opsonic killing of poorly virulent nonmucoid LPS-rough isolates but not of isogenic strains with either a LPS-smooth or a mucoid phenotype. Antibodies to neutral-polysaccharide antigens also failed to protect neutropenic mice from challenge with modest doses of LPS-smooth P. aeruginosa strains (< 10(3) CFU per mouse), whereas O-antigen-specific antibodies were highly protective. Antibodies to neutral polysaccharides deposited significantly (P = 0.002) more C3 onto LPS-rough strains than did antibodies to O side chains, but this situation was reversed when isogenic LPS-smooth strains were tested. Given that protective immunity against P. aeruginosa must be directed against either nonmucoid LPS-smooth strains or mucoid LPS-rough strains, it appears that antibodies specific to neutral-polysaccharide antigens do not protect against P. aeruginosa infection. Lack of protection is likely due to the ability of both O side chains and mucoid exopolysaccharide (alginate) to interfere with the opsonic killing activity of neutral-polysaccharide-specific antibodies.

A non-hemolytic assay for the activation of the alternative pathway of bovine complement

An assay for assessing activation of the bovine alternative pathway of complement was developed. The assay focused on events on the surface of yeast. Yeast cells were incubated with EGTA-Mg2+ plasma, washed and the yeast-bound complement proteins eluted by 100 mM methylamine. Detection of eluted proteins was achieved by Western blot and ELISA. An ELISA for the quantification of the Bb fragment of factor B was chosen to measure activation of the alternative pathway of complement. Using this system, it was possible to demonstrate the kinetics of deposition of Bb on yeast incubated with plasma samples from individual cattle and to show differences between cattle. We were able to categorize cattle into 'fast or slow amplifiers' of the alternative pathway of complement. We suggest that this classification has implications for host protection against invading microorganisms.

The role of complement in inflammation and phagocytosis

Inflammation and phagocytosis are highly complex events involving many humoral and cellular factors, with complement components playing a key role. As described here by Mike Frank and Louis Fries, complement peptides trigger cell function, aid in the recognition of invading pathogens and regulate the phagocytic process via interactions with specific cell surface receptors.

Infectious diseases associated with complement deficiencies

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.

Systemic lupus erythematosus presenting as pneumococcal septicaemia and septic arthritis

A 50 year old woman presented with pneumococcal septicaemia, septic arthritis, and a lobar pneumonia and was subsequently diagnosed as having systemic lupus erythematosus. The blood film and splenic 99mTc sulphur colloid uptake were normal, although selective functional hyposplenism was shown by the impaired clearance of immunoglobulin coated erythrocytes. Systemic lupus erythematosus presenting with fulminating pneumococcal sepsis in the presence of selective defects in spleen function is previously unreported.

Demonstration of an outer membrane protein with antiphagocytic activity from Pasteurella multocida of avian origin

A strain of Pasteurella multocida of avian origin was found to inhibit phagocytosis of Candida albicans by mononuclear phagocytes in vitro. Whole-cell lysates of P. multocida showed this effect, as did a 50-kilodalton (kDa) protein eluted from sodium dodecyl sulfate-polyacrylamide gels obtained by electrophoresis of whole-cell lysates. Heat, digestion with trypsin, and antibody specific for this 50-kDa protein neutralized the antiphagocytic effects of P. multocida, of the whole-cell lysates, and of the 50-kDa protein itself. Evidence that this protein was in the outer membrane of the bacterial cell included the findings that (i) treatment of encapsulated or unencapsulated P. multocida with trypsin reduced the antiphagocytic effect; (ii) whole-cell lysates prepared from trypsinized, unencapsulated P. multocida had reduced antiphagocytic activity; and (iii) antibody to outer membrane proteins neutralized the antiphagocytic effect. Turkeys given antibodies specific for the 50-kDa outer membrane protein were protected against lethal challenge with P. multocida.

Activation of the alternative complement pathway: clinical application of a new technique to measure fragment Ba

A new laser nephelometric technique for the measurement of the alternative complement pathway fragment Ba has been developed. Activation of the alternative complement pathway was assessed in 16 patients with Gram negative bacteraemia, six with Gram positive bacteraemia, 20 with rheumatoid arthritis, and 18 healthy subjects. Patients with Gram negative bacteraemia had significantly higher values of Ba (median 14.8%) than controls (9.3%) (p less than 0.01), while patients with Gram positive bacteraemia and rheumatoid arthritis had values similar to those of controls (10.1% and 9.5%). The technique proved sensitive and precise, and is suitable for the routine laboratory evaluation of complement activation through the alternative pathway.

C2 deficiency, moderately low IgG2 concentrations and lack of the G2m(23) allotype marker in a child with repeated bacterial infections

C2 deficiency was demonstrated in an 11-year-old boy with a past history of recurrent purulent otitis media, pneumonia, H. influenzae meningitis and S. pneumoniae septicaemia. The major histocompatibility complex haplotypes present, A10, B18, DR2, BF*S, C2*QO, C4*A4, C4*B2 and A28, B18, DR2, BF*S, C2*Q0, C4*A4, C4*B2, were in accord with previous observations in C2 deficiency. The concentrations of C1q, C5, factor B and factor D were in the low normal range and the hemolytic activity of the alternative pathway was slightly decreased. In addition, the patient showed moderately low IgG2 concentrations and lacked the IgG2 subclass marker G2m(23). The findings indicate that the patient's susceptibility to bacterial infections may be due to C2 deficiency in combination with the presence of an IgG allotype associated with impaired antibody responses to carbohydrate antigens.

Passive immunization with antibodies against iron-regulated outer membrane proteins protects turkeys from Escherichia coli septicemia

Escherichia coli septicemia is a common disease of young poultry and several species of mammals. Rabbit antiserum was prepared against iron-regulated outer membrane proteins of E. coli. Eighteen-day-old turkeys were passively immunized with antiserum and challenged by air sac inoculation of 1 X 10(6) to 2 X 10(6) CFU of E. coli O78:K80:H9. Turkeys injected with normal rabbit serum or saline solution before challenge served as controls. Fatalities (8 of 51 turkeys inoculated) occurred only in groups given saline solution or normal rabbit serum. The remaining turkeys were necropsied 96 h after challenge. Passive immunization with antiserum significantly (P less than 0.05) reduced the frequency of bacteremia at 96 h after challenge, the frequency of recovery of E. coli from air sacs, and the severity of gross lesions in inoculated birds as compared with birds given normal rabbit serum or saline solution.

Inherited deficiencies of complement and complement-related proteins

The complement cascade and cell-surface proteins related to the complement system are critically important to host defense, immune complex catabolism, and possibly immunoregulation. Genetically determined deficiency states have been described for many complement proteins as well as for fluid phase and cell-borne inhibitors of the complement cascade and cellular complement receptors. Autoimmune diseases and enhanced susceptibility to infection are the dominant clinical manifestation of these deficiencies. Classical pathway deficiencies and low numeric expression of erythrocyte C3b receptors (CR1) are typically associated with autoimmune disorders, while alternative pathway, terminal component, and leukocyte iC3b receptor (CR3) defects predispose to pyogenic bacterial disease. This distinction is not absolute, however, and both classes of disease may appear in most of the reported deficiency states. Specific pharmacologic therapy exists for C1-inhibitor deficiency (hereditary angioedema). Management of other complement deficiencies currently involves sustained diagnostic suspicion and meticulous management of complicating diseases.

Complement subcomponent C1q secreted by cultured human monocytes has subunit structure identical with that of serum C1q

An enzyme-linked immunosorbent assay (e.l.i.s.a.) that is capable of quantifying C1q concentrations as low as 2 ng/ml and a sensitive haemolytic assay were used to study the appearance of material that cross-reacts with human serum C1q as well as C1q haemolytic activity in human monocyte culture media. This material was detected in the medium after 10-14 days and continued to be secreted through to day 28 of culture, at which time the cultures were terminated. Material specifically immunoabsorbed with Sepharose-anti-C1q antibody from a culture medium of cells that was metabolically labelled with [3H] proline or [35S] methionine demonstrated a polypeptide pattern identical with that of serum C1q on SDS/polyacrylamide-gel electrophoresis. Under non-reducing conditions two protein bands were detected migrating with the same Rf values as the serum C1q A-B and C-C dimers. On reduction three bands were evident, which migrated identically with the A, B and C chains of serum C1q. The amount of radioactivity in these bands increased with time in culture, consistent with the e.l.i.s.a. and haemolytic C1q assays. These bands were reactive with monospecific anti-C1q antibody after transfer to nitrocellulose.

Complement effector mechanisms in health and disease

Complement is an effector system able to mediate a number of biological activities in vitro and in vivo. Most familiar is the ability of the system to mediate the lytic destruction of numerous kinds of cells and pathogenic organisms including bacteria, viruses, and virus-infected cells. In addition, the complement system also activates neutrophils, monocytes, basophils, mast cells, and lymphocytes to perform specialized functions. While generally considered to be confined to the effector side of immune reactions, recent evidence indicates that the complement system also directly recognizes and is triggered by a number of bacteria and viruses as well as virus-infected cells in the absence of antibody. In such reactions, complement fulfills the recognition role normally associated with the antibody molecule or immune lymphocyte. The complement system may thus also function as a natural surveillance system operative prior to the induction of specific immunity. Involvement of the complement system in biological reactions has been ascertained by several techniques over the years. These include quantitation of individual complement components in human sera and demonstration of complement deposition in diseased tissues in human diseases and in experimental diseases in animals. Such techniques, however, have limitations in specificity and sensitivity. Assays which detect specific features of the complement activation process have become available in recent years. These tests detect the physical, chemical, or antigenic changes characteristic of the complement activation process. These assays are extremely specific and quantitative; furthermore, most are usable with samples from patients. Three general approaches have been utilized to develop such specific quantitative assays for complement activation. The first includes assays which quantitate activation-specific limited proteolysis of the complement components. The second type of assay includes tests which detect and quantitate new antigens or other activation-specific antigenic changes. The third category is represented by assays which detect and quantitate the protein-protein complexes characteristic of the activation process. Examples of tests presenting each of these approaches are given.(ABSTRACT TRUNCATED AT 400 WORDS)

Inflammation and mediators of lung injury

This article covers the major pathways involved in acute inflammation in mammals with a particular emphasis on their relevance to the bovine species. It focuses on the potential and proven contributions of these systems to pulmonary defense mechanisms and lung pathology. The article also points out what is known and where gaps in our information exist as well as promising areas for research in the coming years.