Interactions between macrophages of guinea pigs and salmonellae. 3. Bactericidal action and cytophilic antibodies of macrophages of infected guinea pigs

Expression of the receptor for IgM (FcμR) by bovine neutrophils

Bovine neutrophils possess a particular set of receptors for immunoglobulins. They have been shown to express a distinctive receptor for IgG2, and it has long been known that they interact poorly with IgG1 but that they can use IgM antibodies as opsonins. We show that the binding of labeled IgM was inhibited by unlabeled IgM but not by IgA, suggesting that bovine neutrophils express a specific IgM receptor. The binding of non-aggregated IgM is strong at 4 °C, but shedding occurs at 37 °C. We designed anti-peptide antibodies based on the sequence of the FcμR, the newly described receptor for IgM. These antibodies bound to bovine neutrophils at 4 °C. At 37 °C, labeling was lost, but the loss was inhibited by pretreatment with cytochalasin D, indicating internalization of the receptor after cross-linking by antibodies. Neutrophils that had internalized the receptor were no longer able to bind IgM. Eosinophils showed a low level of FcμR expression. FcμR expression by neutrophils was not increased by stimulation with Toll-like receptor agonists or the complement anaphylatoxin C5a, and decreased by TNF-α. Exposure of neutrophils to IFN-γ for 18 h increased FcμR expression without augmenting the binding of IgG1 or IgG2. We confirmed that bovine neutrophils can use IgM to phagocytose and kill bacteria without the help of Complement. Neutrophils that have migrated into the lumen of inflamed lactating mammary glands expressed the FcμR. These results indicate that bovine neutrophils express an IgM receptor, the FcμR, which is functional to contribute to the opsonophagocytosis of bacteria at inflammatory sites. Expression of the FcμR by neutrophils gives IgM a particular importance for the immune defense in the bovine species.

HF, S. AS. ULTRASTRUCTURAL CHANGES OF THE MESENTRIC LYMPH NODES OF CALVES EXPERIMENTALLY INFECTED WITH SALMONELLA TYPHIMURIUM

A systemic study was done on the pathogenesis of experimentally induced Salmonella typhimurium infection in calves. The present investigation was carried out on sixteen normal colostrum fed friesian calves, ranging in age from 3 to 6 weeks. The calves were divided into two equal groups. Group I inoculated orally with (1.5 x 10'') Salmonella typhimurium and group IA served as control.  • The early ultrastructural alteration in the mesenteric lymph nodes was the presence of many free Salmonella in localized vacuoles. The interaction between the host cells and phagocytized Salmonella was also observed.

Characterisation of a live Salmonella vaccine stably expressing the Mycobacterium tuberculosis Ag85B-ESAT6 fusion protein

A recombinant Salmonella enterica serovar Typhimurium (S. Typhimurium) vaccine strain was constructed that stably expressed the Mycobacterium tuberculosis fusion antigen Ag85B–ESAT6 from the chromosome. Live oral vaccination of mice with the Salmonella/Ag85B–ESAT6 strain generated a potent anti-Ag85B–ESAT6 T_H1 response with high antibody titres with a IgG2a-bias and significant IFN-γ production lasting over a 120-day period. When mice primed with the Salmonella/Ag85B–ESAT6 vaccine were mucosally boosted with the Ag85B–ESAT6 antigen and adjuvant the IFN-γ responses increased markedly. To determine the protective efficacy of this vaccine strain, guinea pigs were immunised and followed for a 30-week period after aerosol challenge with M. tuberculosis. The heterologous prime-boost strategy of live Salmonella vaccine followed by a systemic boost of antigen and adjuvant reduced the levels of M. tuberculosis bacteria in the lungs and spleen to the same extent as BCG. Additionally, this vaccination regimen was observed to be statistically equivalent in terms of protection to immunisation with BCG. Thus, live oral priming with the recombinant Salmonella/Ag85B–ESAT6 and boosting with Ag85B–ESAT6 plus the adjuvant LTK63 represents an effective mucosal vaccination regimen.

Effect of experimental zinc deficiency on immunological responses in Salmonella-infected guinea-pigs

Cellular and humoral immune responses to Salmonella dublin infection were studied in guinea-pigs given zinc-deficient (ZnD) or zinc-adequate (ZnA) diet, containing 1.03 or 52.4 mg Zn/kg, respectively. On day 30, each animal of each dietary group was inoculated intraperitoneally with 10(6)viable cells of S. dublin strain 493. On the 15th day after infection, the immune responses were assessed by skin hypersensitivity (SH) tests and enzyme-linked immunosorbent assay (ELISA) for serum antibody with Salmonella -extract antigen. ZnD animals had significantly decreased ability to produce Salmonella -specific immediate and delayed type SH responses. These results were further substantiated by histological examination of skin sections. The ELISA indicated significantly lower Salmonella -specific serum antibody titres in ZnD animals than in ZnA animals. Mean viable counts of S. dublin in the liver and spleen of ZnD animals were significantly higher than those in ZnA animals.

Experimental salmonellosis in guinea-pigs: haematological and biochemical studies

Some haematological and biochemical parameters were studied in guinea-pigs infected intraperitoneally with Salmonella dublin 493 at 1 x 10(6) viable cells per animal. The infected animals showed a rise in temperature within 24 h, followed by depression and loss of body weight. On the 15th day post infection, haematological studies revealed a significant increase in the total leukocyte count due to both lymphocytosis and neutrophilia, and a decrease in the total erythrocyte count and haemoglobin concentration. There was also a significantly higher mean corpuscular volume and lower mean corpuscular haemoglobin concentration, indicating a macrocytic hypochromic anaemia. The infection caused a significant increase in alanine aminotransferase activity and creatinine, blood urea nitrogen and globulin concentrations, and a decrease in albumin and triiodothyronine. There was no significant effect on serum total protein or on thyroxine, or in the activity of aspartate aminotransferase in the serum.

Production of IL-1 beta and IL-6 by adherent spleen cells after the stimulation with lipopolysaccharides from Salmonella enteritidis strain

Three different procedures were used to isolate lipopolysaccharides from the Salmonella enteritidis strain 477: phenol-water extraction with ethanol precipitation (LPS 1), phenol-water extraction with methanol precipitation (LPS 2) and FPLC purification (LPS 1/1). Production of interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) was observed in the supernatants of adherent spleen cells of BALB/c mice after the stimulation and cultivation of the cells. The quantity of IL-1 beta and IL-6 depended on the method of LPS isolation. The highest level of IL-1 beta was recorded at LPS 2, and of IL-6 at the stimulation of cells by means of LPS 1.

Protective capacity of L-form Salmonella typhimurium against murine typhoid in C3H/HeJ mice

L forms of Salmonella typhimurium LT2 conferred strong protection to a lethal challenge with its parental bacterium on innately hypersusceptible C3H/HeJ mice, and its minimal protective dose was approximately 150 L-forming units. Although L-form S. typhimurium was avirulent for C3H/HeJ mice, it multiplied slowly in both the liver and spleen with the maximal growth 2-3 weeks after immunization and thereafter it persisted in the liver until 24 weeks. Protective immunity began to work between 4 and 6 weeks after immunization, and it remained active as long as the L forms colonized the liver (until 24 weeks after immunization). Vaccination with the L form induced a population of T cells responding to L-form whole-cell lysate (WCL), while delayed-type hypersensitivity (DTH) to the extract of S. typhimurium was induced after the establishment of solid immunity. Moreover, neither T-cell responses nor DTH to heat-killed S. typhimurium was generated. In addition, antibody responses were elicited to WCL but not to heat-killed S. typhimurium. These results indicate that protection conferred by the L forms is attributable to the persistent colonization of the L forms rather than the presence of DTH, and also that Salmonella cytoplasmic antigens are involved in induction of immunological responses by vaccination with the L forms.

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.

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.

Electron microscopic studies on the location of bacterial proliferation in the liver in murine salmonellosis

Highly susceptible inbred male C57BL/6 mice were infected with 2 X 10(7) virulent Salmonella typhimurium by intraperitoneal inoculation. Samples of the liver were removed 2 or 3 days post-infection for examination by electron microscopy. Rapid infiltration of polymorphs and macrophages was observed in the site of infection. Visual evidence is presented to confirm the destruction of salmonellae within these inflammatory phagocytes as previously reported. The proliferation of the pathogens occurred in the extracellular locations of sinusoids and early lesions, and within hepatocytes.

Role of thymus-derived lymphocytes in acquired immunity to salmonellosis in mice

The relative role of thymus-derived (T-) lymphocytes and bone marrow-derived (B-) cells in acquired immunity to salmonellosis was examined in mice. The results demonstrate that the protective capacity of the donor immunized mice could be passively transferred to the recipient mice by spleen cells but not with peritoneal exudate cells or sera. A high cell number of spleen cells (2 X 10(8)/mouse) were required before passive transfer of immunity could be obtained. Of the T-lymphocytes and B-cell populations of spleen cells, T-cells from immune mice were effective in conferring protection to the recipient mice.

Histopathological study of protective immunity against murine salmonellosis induced by killed vaccine

Swiss-Webster mice were vaccinated with heat-killed salmonellae and then were infected with virulent Salmonella typhimurium. Only 1 of the 18 vaccinated mice died from a challenge of 10(4) X the 50% lethal dose, and about 70% of them survived a challenge of 10(5) X the 50% lethal dose. Histopathological examinations of the lesions developed in these vaccinated mice showed that they followed the characteristic features of a primary lesion in murine salmonellosis. There was an early necrosis with infiltration of polymorphonuclear leukocytes and abscess formation within the first 6 to 7 days after infection. However, these abscesses remained small and discrete. By days 7 to 10, the lesions began to transform into granulomas, first with the appearance of peripheral mononuclear cells and then by the replacement of polymorphs. By the third week of the infection, minute and discrete granulomas were seen scattered in the spleen, liver, and lymph nodes. Beyond this stage, healing and tissue regeneration followed. Thus, the characteristics of infectious lesions developed in mice vaccinated with heat-killed salmonellae are distinctly different from those developed in mice protected by the avirulent vaccine.

The comparative histopathology of primary and secondary lesions in murine salmonellosis

In a primary infection, Swiss-Webster mice were injected i.p. with 10(2) or 10(3) virulent Salmonella typhimurium. Multiple microscopic acute abscesses with predominantly polymorphonuclear leucocytes (PMNs) were seen in the liver and the spleen beginning on the 4th day after infection. By the 7th day, these lesions had become enlarged and were gradually transformed into granulomas with central necrosis and peripheral mononuclear cells. The animals usually died within 12 days with massive systemic infection and degeneration of the tissues. In contrast, it was necessary to inoculate 10(6) virulent salmonella i.v. into mice immunized with avirulent S. thphimurium in order to initiate microscopically observable lesions in the liver and the spleen. These secondary lesions were characterized by the early appearance of minute granulomas composed almost entirely of histiocytic cells. They remained small and isolated, usually without central necrosis. Subsequent regression of the lesions and regeneration of normal tissue occurred after the 2nd week following infection. The animals usually survived such a challenge infection.

Immuno-stimulation by a ribosomal vaccine associated with a bacterial cell wall adjuvant in humans

We have studied a new vaccine of ribosomal nature associated with glycoprotein cell walls from Klebsiella pneumoniae which served as an immunoadjuvant. Thus vaccine was administered by the aerosol route to working men free of any important disease, especially of respiratory disease. A total of 104 men working for the Commissariat à l'Energie Atomique, all volunteers, were randomly placed into two groups. During the first period, 51 patients (group I) were vaccinated three times a week during 5 weeks, and the second group was used as control. During the second period, which started on day 225, the control group received the vaccine, and the first group was revaccinated. Results of this experience show a significant difference in the immunity of the two groups. The specific antibodies increased with vaccination as illustrated by chi-square test (Yates correction), which corresponds to an independent probability equal to 0 (P = 0.5 X 10-4).

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.

Mechanisms of immunity in typhus infections. VI. Differential opsonizing and neutralizing action of human typhus rickettsia-specific cytophilic antibodies in cultures of human macrophages

Human peripheral blood monocytes were incubated in vitro for 6 days to allow time for transformation into macrophage-like cells. Cytophilic antibodies in typhus convalescent human serum were demonstrated by addition of Rickettsia mooseri or Rickettsia prowazeki to passively sensitized human peripheral blood monocyte-derived macrophages that were held at 4 degrees C. Rosettes of rickettsiae were found around macrophages sensitized with immune serum but not around macrophages that had been incubated with normal serum. Inhibition of rosette formation occurred if the macrophages were maintained in normal human serum before addition of immune human serum. Rosettes of R. mooseri were also formed around monocytes obtained from an individual infected with R. mooseri. If the antibody-sensitized macrophages were maintained at 34 degrees C, enhanced phagocytosis of R. mooseri or R. prowazeki occurred as compared with macrophages exposed to normal human serum before infection. However, the cytophilic antibody did not significantly inhibit the subsequent growth of R. prowazeki within the macrophages. This is in contrast to results obtained when R. prowazeki was mixed with immune serum before addition to the macrophage. In the latter case, growth of R. prowazeki was largely inhibited. The significance of antibody cytophilic for macrophages in typhus infections is discussed.

The effect of cytophilic IgG2 on phagocytosis by ovine polymorphonuclear leucocytes

Non-lactating, multiparous ewes were immunized either by subcutaneous infection with live Staphylococcus aureus (seventeen ewes) or by intramuscular injections of a killed S. aureus-oil adjuvant vaccine (seventeen ewes). Polymorphs which were subsequently collected from the mammary glands of the animals were used in in vitro phagocytosis assays against Pseudomonas sp. or S. aureus. There was no difference between polymorphs from the two groups of ewes in their ability to phagocytose Pseudomonas organisms. Polymorphs from the infected ewes showed significant phagocytic superiority over cells from ewes given the killed vaccine when S. aureus was the target organism. This phagocytic superiority could be abrogated by removal of cytophilic immunoglobulin from polymorphs and restored by replacement of cytophilic immunoglobulin. It was shown by staining polymorphs with FITC-conjugated anti-immunoglobulin sera that cytophilic immunoglobulin on the surface of polymorphs belonged to the IgG2 class of immunoglobulins. When 'neutral' polymorphs (from non-immunized ewes) were coated with IgG2 purified from the sera of infected ewes, they exhibited enhanced phagocytosis of staphylococci compared with 'neutral' polymorphs carying IgG2 from the sera of ewes given the killed vaccine.

Specific macrophage immunity to Sendai virus: macrophage aggregation in vitro with Sendai virus by cytophilic antibodies

When a 24-h tube culture of rabbit alveolar macrophages was infected with Sendai virus, the rate of infected cells was found to be limited. Even at a multiplicity of infection (MOI) of 500 plaque-forming units per cell, an average of 63% cells was found to synthesize viral antigens stainable by direct immunofluorescence. When the macrophages obtained from rabbits hyperimmunized by an intravenous injection of Sendai virus were infected under the same in vitro conditions, the rate of antigen synthesis averaged a low as 23%. At the time of infection of alveolar macrophages from immunized rabbits (immune macrophages), cell aggregation at an MOI 50 and cell fusion at an MOI 500 were found 24 h after infection, and these reactions were never encountered after the infection of nonimmune macrophages. When the immune macrophages were either pretreated by trypsin or incubated in medium at pH 4.0, the infection no longer caused the aggregation. The supernatant fluid obtained after incubation at pH 4.0 contained neutralizing antibody to Sendai virus. Conversely, when nonimmune macrophages were incubated in the presence of rabbit anti-Sendai virus serum or purified immunoglobulin G, the same aggregation reaction occurred after virus infection. Ultraviolet light-killed Sendai virus could be used as the counterpart of alive virus in the same aggregation reaction. These results suggest that the aggregation reaction of the immune macrophages could be attributed to the presence of specific cytophilic antibodies on their surface.

Cellular and humoral aspects of host resistance in murine salmonellosis

Mice were challenged with a highly virulent strain of Salmonella typhimurium by intraperitoneal injections. At relatively low infecting doses, immunizations with either viable attenuated or heat killed Salm. typhimurium were found to be equally protective against otherwise fatal infections. Pre-opsonization of virulent salmonellae significantly increased the survival rate of mice infected with small numbers of the pathogen. By a cell culture method, peritoneal macrophages of mice were shown to be innately capable of destroying the ingested virulent Salm. typhimurium. Macrophages from previously infected mice did not appear to have any significant increase in their bactericidal activity against salmonellae, but they possessed cytophilic antibodies specific against the H and the O antigens of Salm. typhimurium. It is believed that humoral elements play an important role in acquired immunity in murine salmonellosis by opsonization of the pathogen.