Brucella abortus inhibits IFN-γ-induced FcγRI expression and FcγRI-restricted phagocytosis via toll-like receptor 2 on human monocytes/macrophages

Brucella infection and Toll-like receptors

Brucella consists of gram-negative bacteria that have the ability to invade and replicate in professional and non-professional phagocytes, and its prolonged persistence in the host leads to brucellosis, a serious zoonosis. Toll-like receptors (TLRs) are the best-known sensors of microorganisms implicated in the regulation of innate and adaptive immunity. In particular, TLRs are transmembrane proteins with a typical structure of an extracellular leucine-rich repeat (LRR) region and an intracellular Toll/interleukin-1 receptor (TIR) domain. In this review, we discuss Brucella infection and the aspects of host immune responses induced by pathogens. Furthermore, we summarize the roles of TLRs in Brucella infection, with substantial emphasis on the molecular insights into its mechanisms of action.

Bispecific antibodies revolutionizing breast cancer treatment: a comprehensive overview

Breast cancer (BCa) is known as a complex and prevalent disease requiring the development of novel anticancer therapeutic approaches. Bispecific antibodies (BsAbs) have emerged as a favorable strategy for BCa treatment due to their unique ability to target two different antigens simultaneously. By targeting tumor-associated antigens (TAAs) on cancer cells, engaging immune effector cells, or blocking critical signaling pathways, BsAbs offer enhanced tumor specificity and immune system involvement, improving anti-cancer activity. Preclinical and clinical studies have demonstrated the potential of BsAbs in BCa. For example, BsAbs targeting human epidermal growth factor receptor 2 (HER2) have shown the ability to redirect immune cells to HER2-positive BCa cells, resulting in effective tumor cell killing. Moreover, targeting the PD-1/PD-L1 pathway by BsAbs has demonstrated promising outcomes in overcoming immunosuppression and enhancing immune-mediated tumor clearance. Combining BsAbs with existing therapeutic approaches, such as chemotherapy, targeted therapies, or immune checkpoint inhibitors (ICIs), has also revealed synergistic effects in preclinical models and early clinical trials, emphasizing the usefulness and potential of BsAbs in BCa treatment. This review summarizes the latest evidence about BsAbs in treating BCa and the challenges and opportunities of their use in BCa.

Brucella abortus RNA does not polarize macrophages to a particular profile but interferes with M1 polarization

Monocytes and macrophages play a central role in chronic brucellosis. Brucella abortus (Ba) is an intracellular pathogen that survives inside these cells. On the other hand, macrophages could be differentiated into classical (M1), alternative (M2) or other less-identified profiles. We have previously shown that Ba RNA (a bacterial viability-associated PAMP or vita-PAMP) is a key molecule by which Ba can evade the host immune response. However, we did not know if macrophages could be polarized by this vita-PAMP. To assess this, we used two different approaches: we evaluated if Ba RNA per se was able to differentiate macrophages to M1 or M2 or, given that Ba survives inside macrophages once a Th1 response is established (i.e., in the presence of IFN-γ), we also analysed if Ba RNA could interfere with M1 polarization. We found that Ba RNA alone does not polarize to M1 or M2 but activates human macrophages instead. However, our results show that Ba RNA does interfere with M1 polarization while they are being differentiated. This vita-PAMP diminished the M1-induced CD64, and MHC-II surface expression on macrophages at 48 h. This phenomenon was not associated with an alternative activation of these cells (M2), as shown by unchanged CD206, DC-SIGN and CD163 surface expression. When evaluating glucose metabolism, we found that Ba RNA did not modify M1 glucose consumption or lactate production. However, production of Nitrogen Reactive Species (NRS) did diminish in Ba RNA-treated M1 macrophages. Overall, our results show that Ba RNA could alter the proper immune response set to counterattack the bacteria that could persist in the host establishing a chronic infection.

Brucella Outer Membrane Lipoproteins 19 and 16 Differentially Induce IL-18 Response or Pyroptosis in Human Monocytic Cells

BACKGROUND

Brucella species (B. spp.) are Gram-negative intracellular bacteria, causing severe inflammatory diseases in animals and humans. Two major lipoproteins (L19) and (L16) of Brucella outer membrane proteins (OMPs) were extensively explored in associating with inflammatory response of human monocytes (THP-1).

METHODS

Activated THP-1 cells induced with recombinant L19 and L16 were analyzed in comparison with unlipidated forms (U19 and U16) and lipopolysaccharide (LPS) of B. melitensis, respectively.

RESULTS

Secretion of inflammatory factors TNF-α, IL-6 and IL-1β was significantly increased from L19, L16 or both stimulated THP-1 cells. High secretion of IL-18 was detected only from L19-induced cells. Signaling of those cytokine responses was identified mainly through P38-MAPK pathway, and signaling of L19-induced IL-1β response was partly occurred via NF-κB. Exploration for different forms of IL-18 found that L19-induced production of active IL-18 (18 kD) was through up-regulating NLRP3 and activating caspase-1, while L16-induced production of inactive IL-18 fragments (15 kD and 16 kD) occurred through activating caspase-8/3. Additionally, L19 up-regulated phosphorylation of XIAP for inhibiting caspase-3 activity to cleave IL-18, while L16 activated caspase-3 for producing GSDME-N and leading to pyroptosis of THP-1 cells.

CONCLUSION

Brucella L19 and L16 differentially induce IL-18 response or pyroptosis in THP-1 cells, respectively.

The Mechanism of Facultative Intracellular Parasitism of Brucella

Brucellosis is a highly prevalent zoonotic disease characterized by abortion and reproductive dysfunction in pregnant animals. Although the mortality rate of Brucellosis is low, it is harmful to human health, and also seriously affects the development of animal husbandry, tourism and international trade. Brucellosis is caused by Brucella, which is a facultative intracellular parasitic bacteria. It mainly forms Brucella-containing vacuoles (BCV) in the host cell to avoid the combination with lysosome (Lys), so as to avoid the elimination of it by the host immune system. Brucella not only has the ability to resist the phagocytic bactericidal effect, but also can make the host cells form a microenvironment which is conducive to its survival, reproduction and replication, and survive in the host cells for a long time, which eventually leads to the formation of chronic persistent infection. Brucella can proliferate and replicate in cells, evade host immune response and induce persistent infection, which are difficult problems in the treatment and prevention of Brucellosis. Therefore, the paper provides a preliminary overview of the facultative intracellular parasitic and immune escape mechanisms of Brucella, which provides a theoretical basis for the later study on the pathogenesis of Brucella.

Uncovering the Hidden Credentials of Brucella Virulence

Bacteria in the genus Brucella are important human and veterinary pathogens. The abortion and infertility they cause in food animals produce economic hardships in areas where the disease has not been controlled, and human brucellosis is one of the world's most common zoonoses. Brucella strains have also been isolated from wildlife, but we know much less about the pathobiology and epidemiology of these infections than we do about brucellosis in domestic animals. The brucellae maintain predominantly an intracellular lifestyle in their mammalian hosts, and their ability to subvert the host immune response and survive and replicate in macrophages and placental trophoblasts underlies their success as pathogens. We are just beginning to understand how these bacteria evolved from a progenitor alphaproteobacterium with an environmental niche and diverged to become highly host-adapted and host-specific pathogens. Two important virulence determinants played critical roles in this evolution: (i) a type IV secretion system that secretes effector molecules into the host cell cytoplasm that direct the intracellular trafficking of the brucellae and modulate host immune responses and (ii) a lipopolysaccharide moiety which poorly stimulates host inflammatory responses. This review highlights what we presently know about how these and other virulence determinants contribute to Brucella pathogenesis. Gaining a better understanding of how the brucellae produce disease will provide us with information that can be used to design better strategies for preventing brucellosis in animals and for preventing and treating this disease in humans.

Adenosine receptor Adora2b antagonism attenuates Brucella abortus 544 infection in professional phagocyte RAW 264.7 cells and BALB/c mice

Brucella as a stealthy intracellular pathogen avoids activation of innate immune response. Here we investigated the contribution of an adenosine receptor, Adora2b, during Brucella infection in professional phagocyte RAW 264.7 cells and in a murine model. Adora2b-deficient cells showed attenuated Brucella internalization and intracellular survival with enhanced release of IL-6, TNF-α, IL-12 and MCP-1. In addition, blockade of Adora2b using MRS 1754 treatment in mice resulted in increased total weight of the spleens but suppressed bacterial burden in these organs accompanied by elevated levels of IL-6, IFN-γ, TNF-α, IL-12 and MCP-1, while reduced IL-10. Overall, we proposed that the Adora2b participates in the successful phagocytic pathway and intracellular survival of Brucella in RAW 264.7 cells, and could be a potential therapeutic target for the treatment of acute brucellosis in animals.

Evaluation of the General Organization of Veterinary Services control program of animal brucellosis in Egypt: An outbreak investigation of brucellosis in buffalo

BACKGROUND AND AIM

Brucellosis is a major constraint to livestock production in Egypt as well as many developing countries worldwide. Bovine brucellosis is an economically important disease with reproductive failure as a principal manifestation resulting in abortion, premature birth and decreased milk production in females, and orchitis and epididymitis in males. In spite of the efforts of Egyptian veterinary services to overcome brucellosis, the disease is still prevalent in both animals and humans and represents one of the most important public health hazards in Egypt. The aim of the present work was to investigate the efficacy of the control program implemented by the General Organization of Veterinary Services in Brucella infected buffalo farm on serological, molecular, cultural, and histopathological basis. Brucella melitensis biovar 3 was recovered from 6 buffalo-cows.

MATERIALS AND METHODS

Blood samples were collected from a total of 750 non-vaccinated lactating buffalo-cows. These animals were proved positive for Brucella by the Egyptian brucellosis national program. Sera were tested using buffered acidified plate antigen test and rose Bengal test as screening tests and complement fixation test as a confirmatory test. Positive animals were separated for slaughtering under the supervision of the Egyptian veterinary authorities. Remaining animals were tested every 3 weeks with slaughtering of positive cases and this continued until the remaining animals revealed three successive negative serological tests. Different lymph nodes (prescapular, prefemoral, mediastinal, retropharyngeal, and supramammary) were collected from 11 Brucella seropositive buffalo-cows slaughtered after being confirmed serologically as Brucella infected cases. Samples were collected and processed for bacterial isolation and nucleic acid detection using polymerase chain reaction (PCR). Parts of these specimens were fixed in 10% neutral buffered formalin for 48 h then processed by paraffin embedding technique.

RESULTS

"Test and slaughter" policy was applied on Brucella infected dairy buffalo farm. The program continued for 6 months with slaughtering of positive cases until the herd was proved Brucella free. B. melitensis biovar 3 could be recovered from six buffalo-cows. Universal PCR confirmed Brucella on genus level and Bruce-ladder multiplex, PCR confirmed the presence of B. melitensis on the species level. Histopathological examination of Brucella-infected lymph nodes revealed massive rarified and depleted lymphoid areas of both sub-capsular and deep cortical lymphoid follicles, macrophage cells granulomatous reaction, as well as fat, infiltrates, and chronic vasculitis. The chronic nature of Brucella lesions has been confirmed in this study as indicated by the chronic vasculitis and collagen deposition.

CONCLUSION

Freedom status from brucellosis in this study required 6 months which are considered long time allowing the spread of infection to other localities especially under unhygienic conditions, husbandry system favoring mixed populations of different ages, sex, aborted and pregnant, and lack of controlled movement of animals. Therefore, effective control of animal brucellosis requires surveillance to identify infected animal herds, elimination of the reservoirs, and vaccination of young heifers. B. melitensis biovar 3 is the cause of the Brucella outbreak in buffalo which still remains the prevalent type of Brucella in Egypt. The disease runs a chronic course allowing further spread of infection.

Brucella Omp25 Upregulates miR-155, miR-21-5p, and miR-23b to Inhibit Interleukin-12 Production via Modulation of Programmed Death-1 Signaling in Human Monocyte/Macrophages

Brucella spp. infection results in compromised Type1 (Th1) cellular immune response. Several reports have described an immunomodulatory function for Brucella major outer membrane protein Omp25. However, the mechanism by which Omp25 modulates macrophage dysfunction has not been defined. Herein, we reported that Omp25-deficient mutant of Brucella suis exhibited an enhanced ability to induce interleukin (IL)-12 whereas ectopic expression of Omp25 protein inhibited TLR agonists-induced IL-12 p70 production through suppression of both IL-12 p40 and p35 subunit expression in THP-1 cells. In addition, Omp25 significantly upregulated miR-155, -23b and -21-5p, as well as the immunomodulator molecule programmed death-1 (PD-1) in monocyte/macrophages. The upregulation of miR-155 and -23b correlated temporally with decreased TAB2 levels, IκB phosphorylation and IL-12 p40 levels by targeting TAB2 and il12B 3' untranslated region (UTR), respectively, while miR-21-5p increase directly led to the reduction of lipopolysaccharide (LPS)/R848-induced IL-12 p35 protein by targeting il12A 3'UTR. Consistent with this finding, reduction of miR-155 and -23b attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p40 expression at both transcriptional and posttranscriptional levels, while reduction of miR-21-5p attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p35 expression at the posttranscriptional level, together significantly enhanced IL-12 p70 production upon LPS/R848 stimulation. We also found that blocking PD-1 signaling decreased the expression of miR-155, -23b and -21-5p induced by Omp25 and enhanced IL-12 production in monocyte/macrophages. Altogether, these data demonstrate that Brucella Omp25 induces miR-155, -23b and -21-5p to negatively regulate IL-12 production at both transcriptional and posttranscriptional levels via regulation of PD-1 signaling, which provides an entirely new mechanism underlying monocyte/macrophages dysfunction during Brucella spp. infection.

Key role of Toll-like receptor 2 in the inflammatory response and major histocompatibility complex class ii downregulation in Brucella abortus-infected alveolar macrophages

Alveolar macrophages (AM) seem to constitute the main cellular target of inhaled brucellae. Here, we show that Brucella abortus invades and replicates in murine AM without inducing cytotoxicity. B. abortus infection induced a statistically significant increase of tumor necrosis factor alpha (TNF-α), CXCL1 or keratinocyte chemoattractant (KC), interleukin-1β (IL-1β), IL-6, and IL-12 in AM from C57BL/6 mice and BALB/c mice, but these responses were generally weaker and/or delayed compared to those elicited in peritoneal macrophages. Studies using knockout mice for TLR2, TLR4, and TLR9 revealed that TNF-α and KC responses were mediated by TLR2 recognition. Brucella infection reduced in a multiplicity of infection-dependent manner the expression of major histocompatibility complex class II (MHC-II) molecules induced by gamma interferon (IFN-γ) in AM. The same phenomenon was induced by incubation with heat-killed B. abortus (HKBA) or the lipidated form of the 19-kDa outer membrane protein of Brucella (L-Omp19), and it was shown to be mediated by TLR2 recognition. In contrast, no significant downregulation of MHC-II was induced by either unlipidated Omp19 or Brucella LPS. In a functional assay, treatment of AM with either L-Omp19 or HKBA reduced the MHC-II-restricted presentation of OVA peptides to specific T cells. One week after intratracheal infection, viable B. abortus was detected in AM from both wild-type and TLR2 KO mice, but CFU counts were higher in the latter. These results suggest that B. abortus survives in AM after inhalatory infection in spite of a certain degree of immune control exerted by the TLR2-mediated inflammatory response. Both the modest nature of the latter and the modulation of MHC-II expression by the bacterium may contribute to such survival.

Toll-like receptor 6 plays an important role in host innate resistance to Brucella abortus infection in mice

Brucella abortus is recognized by several Toll-like receptor (TLR)-associated pathways triggering proinflammatory responses that affect both the nature and intensity of the immune response. Previously, we demonstrated that B. abortus-mediated dendritic cell (DC) maturation and control of infection are dependent on the adaptor molecule MyD88. However, the involvement of all TLRs in response to B. abortus infection is not completely understood. Therefore, we decided to evaluate the requirement for TLR6 in host resistance to B. abortus. Here, we demonstrated that TLR6 is an important component for triggering an innate immune response against B. abortus. An in vitro luciferase assay indicated that TLR6 cooperates with TLR2 to sense Brucella and further activates NF-κB signaling. However, in vivo analysis showed that TLR6, not TLR2, is required for the efficient control of B. abortus infection. Additionally, B. abortus-infected dendritic cells require TLR6 to induce tumor necrosis factor alpha (TNF-α) and interleukin-12 (IL-12). Furthermore, our findings demonstrated that the mitogen-activated protein kinase (MAPK) signaling pathway is impaired in TLR2, TLR6, and TLR2/6 knockout (KO) DCs when infected with B. abortus, which may account for the lower proinflammatory cytokine production observed in TLR6 KO mouse dendritic cells. In summary, the results presented here indicate that TLR6 is required to trigger innate immune responses against B. abortus in vivo and is required for the full activation of DCs to induce robust proinflammatory cytokine production.

Progress in Brucella vaccine development

Brucella spp. are zoonotic, facultative intracellular pathogens, which cause animal and human disease. Animal disease results in abortion of fetuses; in humans, it manifests flu-like symptoms with an undulant fever, with osteoarthritis as a common complication of infection. Antibiotic regimens for human brucellosis patients may last several months and are not always completely effective. While there are no vaccines for humans, several licensed live Brucella vaccines are available for use in livestock. The performance of these animal vaccines is dependent upon the host species, dose, and route of immunization. Newly engineered live vaccines, lacking well-defined virulence factors, retain low residual virulence, are highly protective, and may someday replace currently used animal vaccines. These also have possible human applications. Moreover, due to their enhanced safety and efficacy in animal models, subunit vaccines for brucellosis show great promise for their application in livestock and humans. This review summarizes the progress of brucellosis vaccine development and presents an overview of candidate vaccines.

Toll-like receptors are critical for clearance of Brucella and play different roles in development of adaptive immunity following aerosol challenge in mice

Brucella spp. cause undulant fever in humans and brucellosis in variety of other animals. Both innate and adaptive immunity have been shown to be important in controlling Brucella infection. Toll-like receptors (TLRs) represent a group of pattern recognition receptors (PRRs) that play critical roles in the host innate immune response, as well as development of adaptive immunity. In the current report, we investigated the role of TLR signaling in the clearance of Brucella and development of adaptive immunity in TLR2(-/-), TLR4(-/-), or MyD88(-/-) mice following aerosol exposure to B. melitensis 16 M. Consistent with previous reports, MyD88 is required for efficient clearance of Brucella from all three organs (lung, spleen, and liver). The results reveal Th2-skewed immune responses in TLR2(-/-) mice late in infection and support a TLR2 requirement for efficient clearance of Brucella from the lungs, but not from the spleen or liver. Similarly, TLR4 is required for efficient clearance of Brucella from the lung, but exhibits a minor contribution to clearance from the spleen and no demonstrable contribution to clearance from the liver. Lymphocyte proliferation assays suggest that the TLRs are not involved in the development of cell-mediated memory response to Brucella antigen. Antibody detection reveals that TLR2 and 4 are required to generate early antigen-specific IgG, but not during the late stages of infection. TLR2 and 4 are only transiently required for IgM production and not at all for IgA production. In contrast, MyD88 is essential for antigen specific IgG production late in infection, but is not required for IgM generation over the course of infection. Surprisingly, despite the prominent role for MyD88 in clearance from all tissues, MyD88-knockout mice express significantly higher levels of serum IgA. These results confirm the important role of MyD88 in controlling infection in the spleen while providing evidence of a prominent contribution to protection in other tissues. In addition, although TLR4 and TLR2 contribute little to control of spleen infection, a significant contribution to clearance of lung infection is described.

Internal affairs: investigating the Brucella intracellular lifestyle

Bacteria of the genus Brucella are Gram-negative pathogens of several animal species that cause a zoonotic disease in humans known as brucellosis or Malta fever. Within their hosts, brucellae reside within different cell types where they establish a replicative niche and remain protected from the immune response. The aim of this article is to discuss recent advances in the field in the specific context of the Brucella intracellular 'lifestyle'. We initially discuss the different host cell targets and their relevance during infection. As it represents the key to intracellular replication, the focus is then set on the maturation of the Brucella phagosome, with particular emphasis on the Brucella factors that are directly implicated in intracellular trafficking and modulation of host cell signalling pathways. Recent data on the role of the type IV secretion system are discussed, novel effector molecules identified and how some of them impact on trafficking events. Current knowledge on Brucella gene regulation and control of host cell death are summarized, as they directly affect intracellular persistence. Understanding how Brucella molecules interplay with their host cell targets to modulate cellular functions and establish the intracellular niche will help unravel how this pathogen causes disease.

Deep sequencing-based expression transcriptional profiling changes during Brucella infection

Brucellosis is a worldwide zoonotic infectious disease that has significant economic effects on animal production and human health. The host macrophage -Brucella interaction is critical to the establishment of infections. Thus, the kinetic transcriptional profile of gene expression in macrophages infected with the Brucella melitensis strain 16M was investigated in the current study using a technology based on deep sequencing. The total RNA was extracted from macrophages 0, 4, and 24 h post-infection. Data analysis showed that in the gene ontology term, the expression of genes in the endoplasmic reticulum, lysosomes, as well as those involved in programmed cell death and apoptosis significantly changed during the first 24 h post-infection. Pathway enrichment analysis indicated that the genes in the apoptosis pathway, NOD-like receptor signaling pathway, Fc gamma R-mediated phagocytosis, lysosome pathway, p53 signaling pathway, and protein processing in the endoplasmic reticulum significantly changed during the first 24 h post-infection. The B-cell receptor and toll-like receptor signaling pathways were also significantly changed 24 h post-infection compared with those 4 h post-infection. The results of the current study can contribute to an improved understanding of the manner by which host cell responses may be manipulated to prevent Brucella infection.