Diminished T lymphocyte proliferative response to polyclonal mitogens in acute brucellosis patients

Key immunity characteristics of diverse stages of brucellosis in rural population from Inner Mongolia, China

Background

Brucellosis poses a serious threat to human and animal health, particularly in developing countries such as China. The Inner Mongolia Autonomous Region is one of the most severely brucellosis-endemic provinces in China. Currently, the host immune responses functioning to control Brucella infection and development remain poorly understood. The aim of this study is to further clarify the key immunity characteristics of diverse stages of brucellosis in Inner Mongolia.

Methods

We collected a total of 733 blood samples from acute (n = 137), chronic (n = 316), inapparent (n = 35), recovery (n = 99), and healthy (n = 146) groups from the rural community of Inner Mongolia between 2014 and 2015. The proportions of CD4⁺, CD8⁺, Th1, Th2, and Th17 T cells in peripheral blood and the expression of TLR2 and TLR4 in lymphocytes, monocytes and granulocytes were examined using flow cytometry analysis. The differences among the five groups were compared using one-way ANOVA and the Kruskal–Wallis method, respectively.

Results

Our results revealed that the proportions of CD4⁺ and CD8⁺ T cells were significantly different among the acute, chronic, recovery, and healthy control groups (P < 0.05), with lower proportions of CD4⁺ T cells and a higher proportion of CD8⁺ T cells in the acute, chronic, and recovery groups. The proportion of Th1 cells in the acute, chronic, and inapparent groups was higher than that in the healthy and recovery groups; however, there was no significant difference between patients and healthy individuals (P > 0.05). The proportion of Th2 lymphocytes was significantly higher in the acute and healthy groups than in the inapparent group (P < 0.05). The proportion of Th17 cells in the acute group was significantly higher than that in the healthy control, chronic, and inapparent groups (P < 0.05). Finally, the highest expression of TLR4 in lymphocytes, monocytes and granulocytes was observed in the recovery group, and this was followed by the acute, chronic, healthy control, and inapparent groups. There was a significant difference between the recovery group and the other groups, except for the acute group (P < 0.05). Moreover, a correlation in TLR4 expression was observed in lymphocytes, monocytes and granulocytes among the five groups (r > 0.5), except for the inapparent group between lymphocytes and granulocytes (r = 0.34).

Conclusions

Two key factors (CD8⁺ T cells and TLR4) in human immune profiles may closely correlate with the progression of brucellosis. The detailed function of TLR4 in the context of a greater number of cell types or tissues in human or animal brucellosis and in larger samples should be further explored in the future.

Graphical Abstract

Meta-Analysis of the Changes of Peripheral Blood T Cell Subsets in Patients with Brucellosis

Brucellosis is one of the most prevalent zoonotic diseases in the world, but its pathogenesis is not very clear. At present, it is thought that it may be related to the immunity of T cells. The conclusions of related studies are inconsistent, and its clinical significance is not explicit. We searched published articles in electronic databases up to December 2017 identified as relating to the clinical features of human brucellosis in China. Only eight studies had sufficient quality for data extraction. Meta-analysis showed a significantly decreased proportion of CD4+ T cells in human brucellosis patients compared to healthy subject individuals. The frequency of CD8+ T cells was significantly higher in human brucellosis patients than that in the healthy control group. The pooled analysis presented a significant decrease of the CD4+/CD8+ ratio in human brucellosis patients compared to healthy subjects. There is immunologic dysfunction of T lymphocyte in patients with human brucellosis, the CD4+ and CD8+ T cells might be the important factors affecting the progress of brucellosis.

Liver involvement in patients with brucellosis: results of the Marmara study

Brucellosis is a zoonotic disease that primarily affects the reticuloendothelial system. But, the extent of liver damage in due course of the disease is unclear. This study included 325 brucellosis patients with significant hepatobiliary involvement identified with microbiological analyses from 30 centers between 2000 and 2013. The patients with ≥5 times of the upper limit of normal for aminotransferases, total bilirubin level ≥2 mg/dl or local liver lesions were enrolled. Clinical hepatitis was detected in 284 patients (87.3 %) and cholestasis was detected in 215 (66.1 %) patients. Fatigue (91 %), fever (86 %), sweating (83 %), arthralgia (79 %), and lack of appetite (79 %) were the major symptoms. Laboratory tests showed anemia in 169 (52 %), thrombocytopenia in 117 (36 %), leukopenia in 81 (25 %), pancytopenia in 42 (13 %), and leukocytosis in 20 (6 %) patients. The most commonly used antibiotic combinations were doxycycline plus an aminoglycoside (n = 73), doxycycline plus rifampicin (n = 71), doxycycline plus rifampicin and an aminoglycoside (n = 27). The duration of ALT normalization differed significantly in three treatment groups (p < 0.001). The use of doxycycline and an aminoglycoside in clinical hepatitis showed better results compared to doxycycline and rifampicin or rifampicin, aminoglycoside, doxycycline regimens (p < 0.05). However, the length of hospital stay did not differ significantly between these three combinations (p > 0.05). During the follow-up, treatment failure occurred in four patients (1 %) and relapse was seen in three patients (0.9 %). Mortality was not observed. Hepatobiliary involvement in brucellosis has a benign course with suitable antibiotics and the use of doxycycline and an aminoglycoside regimen seems a better strategy in select patients.

Acute infection by conjunctival route with Brucella melitensis induces IgG+ cells and IFN-gamma producing cells in peripheral and mucosal lymph nodes in sheep

The early distribution of Brucella melitensis and the immune response induced in lymphoid tissues and lymph nodes (LN) draining the upper respiratory tract were analysed in sheep. An experimental acute infection was performed by inoculating the sheep with the virulent H38 strain of B. melitensis by the conjunctival route. The infection was rapidly controlled at the site of inoculation but resulted in a local and systemic dissemination of brucellae mainly in the pharyngeal tonsil, local and peripheral LN and the spleen. The control of the infection was associated with the induction of a specific immune response characterized by an increase in IgG+ cells, the production of IFN-gamma and IL-10 by cells from draining parotid, retropharyngeal and submaxillary LN, but also from more distant peripheral prescapular and mesenteric LN. IFN-gamma was produced by CD4+, CD8+ and CD4(-)CD8(-)gammadelta(-) cells and probably contributed to the control of both local and systemic infection.

Brucella abortus inhibits major histocompatibility complex class II expression and antigen processing through interleukin-6 secretion via Toll-like receptor 2

The strategies that allow Brucella abortus to survive inside macrophages for prolonged periods and to avoid the immunological surveillance of major histocompatibility complex class II (MHC-II)-restricted gamma interferon (IFN-gamma)-producing CD4+ T lymphocytes are poorly understood. We report here that infection of THP-1 cells with B. abortus inhibited expression of MHC-II molecules and antigen (Ag) processing. Heat-killed B. abortus (HKBA) also induced both these phenomena, indicating the independence of bacterial viability and involvement of a structural component of the bacterium. Accordingly, outer membrane protein 19 (Omp19), a prototypical B. abortus lipoprotein, inhibited both MHC-II expression and Ag processing to the same extent as HKBA. Moreover, a synthetic lipohexapeptide that mimics the structure of the protein lipid moiety also inhibited MHC-II expression, indicating that any Brucella lipoprotein could down-modulate MHC-II expression and Ag processing. Inhibition of MHC-II expression and Ag processing by either HKBA or lipidated Omp19 (L-Omp19) depended on Toll-like receptor 2 and was mediated by interleukin-6. HKBA or L-Omp19 also inhibited MHC-II expression and Ag processing of human monocytes. In addition, exposure to the synthetic lipohexapeptide inhibited Ag-specific T-cell proliferation and IFN-gamma production of peripheral blood mononuclear cells from Brucella-infected patients. Together, these results indicate that there is a mechanism by which B. abortus may prevent recognition by T cells to evade host immunity and establish a chronic infection.

A B lymphocyte mitogen is a Brucella abortus virulence factor required for persistent infection

Microbial pathogens with the ability to establish chronic infections have evolved strategies to actively modulate the host immune response. Brucellosis is a disease caused by a Gram-negative intracellular pathogen that if not treated during the initial phase of the infection becomes chronic as the bacteria persist for the lifespan of the host. How this pathogen and others achieve this action is a largely unanswered question. We report here the identification of a Brucella abortus gene (prpA) directly involved in the immune modulation of the host. PrpA belongs to the proline-racemase family and elicits a B lymphocyte polyclonal activation that depends on the integrity of its proline-racemase catalytic site. Stimulation of splenocytes with PrpA also results in IL-10 secretion. Construction of a B. abortus-prpA mutant allowed us to assess the contribution of PrpA to the infection process. Mice infected with B. abortus induced an early and transient nonresponsive status of splenocytes to both Escherichia coli LPS and ConA. This phenomenon was not observed when mice were infected with a B. abortus-prpA mutant. Moreover, the B. abortus-prpA mutant had a reduced capacity to establish a chronic infection in mice. We propose that an early and transient nonresponsive immune condition of the host mediated by this B cell polyclonal activator is required for establishing a successful chronic infection by Brucella.

Dominant Th1 cytokine production in early onset of human brucellosis followed by switching towards Th2 along prolongation of disease

Human brucellosis is a worldwide zoonotic infectious disease which is caused by intracellular bacteria belonging to the genus Brucella. Based on murine studies it has been shown that host resistance to Brucella depends on Th1 response, whereas Th2 response is involved in the severity of the disease. Since the immune response during human brucellosis has not been profoundly studied we have tried to evaluate cytokine production in patients suffering from brucellosis. Diluted whole blood samples were cultured in the presence of the mitogen, heat inactivated bacteria or medium alone. IL-12, IFN-gamma and IL-10 were measured by specific sandwich ELISA. In addition, the percentage of CD3(+) T cells producing either IL-13 or IFN-gamma was determined by flow cytometry. It was found that not only IFN-gamma production but also the number of CD3(+) IFN-gamma-producing cells decreased with prolongation of the disease but the percentage of CD3(+) IL-13(+) T cells were significantly increased. No correlation between duration of disease and IL-10 or IL-12 production was found. In conclusion, it is proposed that at the onset of brucellosis, Th1 response dominates while diminishing with prolongation of the disease.

In vitro nonspecific mitogenic response of T-cell subsets in acute and chronic brucellosis

The aim of the present study was to determine the cellular immune response on the course of brucellosis by investigating the proliferation response of T-cell subsets to phytohemagglutinin (PHA), that is, nonspecific mitogen in the patients with acute and chronic brucellosis. The study was performed in 19 patients with untreated brucellosis (acute, n = 11; chronic, n = 8) and 19 healthy controls. Standard tube agglutination and Coombs tests for brucellosis were performed. CD4+ and CD8+ T cell were investigated by the flow cytometry and sorting methods in all of cases. After these cells were cultured and stimulated with PHA, [H3]-thymidine uptake and stimulation indices (SIs) were established. In all of the patients with brucellosis, CD4+ SIs and CD8+ SIs were found to be 1.40 +/- 0.63 and 1.45 +/- 0.42, respectively, and in the controls CD4+ SIs and CD8+ SIs were 1.59 +/- 0.36 and 1.64 +/- 0.37, respectively. In acute cases, CD4+ SIs were 1.71 +/- 0.64 and CD8+ SIs were 1.54 +/- 0.45. CD4+ SIs were 0.97 +/- 0.25 and CD8+ SIs were 1.32 +/- 0.37 in chronic cases. Although in acute cases CD4+ SIs and CD8+ SIs were not different from those in the control group, CD4+ SIs of chronic brucellosis cases were found to be significantly low as compared with those of acute brucellosis cases and the controls (P < 0.01). CD8+ SIs of acute and chronic brucellosis cases were not found to be different from those in the controls. Brucella agglutination titers of the patients with acute and chronic brucellosis were not found related with CD4 SIs and CD8 SIs. The findings of significantly low results of CD4+ T-cell proliferative responses of chronic brucellosis to PHA as compared with control and acute brucellosis cases remind that the development of chronic infection might be a result of T-helper proliferation defect.

Determination of intracellular cytokines produced by Th1 and Th2 cells using flow cytometry in patients with brucellosis

The aim of the study was to evaluate intracellular interferon-gamma (IFN-gamma), and interleukin-4 (IL-4) levels in pre- and post-treatment periods of brucellosis patients and to determine the relationship between these parameters and patients' clinical findings. Twenty-five patients diagnosed as brucellosis and 11 aged-matched healthy volunteers were included in the study. CD3+CD4+ T lymphocytes levels were significantly lower in patients with brucellosis as compared to the control group. CD3+CD8+ T lymphocytes and CD3+IFN-gamma+ levels were increased in brucellosis patients compared with the control group. CD4+IFN-gamma+ and CD4+IL-4+ levels were no different between patients and healthy individuals. CD3+IL-4+ levels decreased in patients compared with healthy controls. Pre-treatment CD3+IFN-gamma+ levels dramatically increased in patients responsive to management compared with the unresponsive ones. In responsive cases, CD3+IFN-gamma+ levels decreased statistically after the treatment while in unresponsive cases no meaningful change was observed with respect to treatment. Adding IFN-gamma to the treatment for improving the depleted levels of IFN-gamma can be beneficial in patients with brucellosis who shows a tendency to chronicity or patients who do not respond to the treatment.

Cellular bioterrorism: how Brucella corrupts macrophage physiology to promote invasion and proliferation

Brucellosis is a worldwide human zoonosis caused by intracellular bacteria of the genus Brucella. Virulence factors play an important role in allowing Brucella infection and proliferation within macrophages. Brucella enters macrophages through lipid raft microdomains, avoids phagolysosome fusion, and inhibits TNF-alpha secretion and apoptosis. Furthermore, Brucella can perturb bactericidal activity in macrophages by influencing the host cell response to its advantage through its LPS or by activating the cAMP/PKA pathway. To date, small steps have been taken in defining and understanding the virulence factors of Brucella used in macrophage subversion, but further investigation is required to fully explain virulence and persistence.

The Effect of the Doxycycline-Rifampicin and Levamisole Combination on Lymphocyte Subgroups and Functions of Phagocytic Cells in Patients with Chronic Brucellosis

BACKGROUND

Brucellosis is one of the important health problems for both humans and animals in Turkey since agriculture and stock raising appears to be the most important means of subsistence. Investigations on the pathogenesis of brucellosis reveal that the etiologic agent can survive in phagocytic cells, and cell-mediated immunity plays an important role in immunity against bacteria.

METHODS

In this study, we investigated whether supplementation of levamisole, a well-known antihelminthic agent with immune-stimulating activity to conventional antibiotic therapy, would improve the anergy against Brucella.

RESULTS

The results of our study reveal that a 6-week course of levamisole as a supplement to conventional antibiotic therapy in chronic brucellosis is not superior to conventional antibiotic treatment alone with respect to lymphocyte subgroup ratios and phagocytic function.

CONCLUSION

In chronic brucellosis, levamisole administered as a supplement concomitantly with conventional antibiotic therapy has no immunostimulating effect on the basis of the lymphocyte subgroups ratios measured and the ability of phagocytosis in the present study. Further large clinical and laboratory trials are necessary to investigate the immunological and physiological effects of levamisole on T(H1) subtypes and cytokine secretion.

The innate immune response against Brucella in humans

Pathogens have developed different strategies to survive and multiply within their host. Among them is the ability to control phagocyte apoptosis while another is to affect the expression of cytokines which is necessary for a normal protective function of the immune response. To establish themselves and cause chronic disease in humans and animals, Brucella spp. invade and proliferate within monocytic phagocytes. We have established that in humans, Brucella suis impairs the apoptosis of monocytes and macrophages, thus preventing its host cell elimination. In mice, which are not naturally colonized by the bacteria, Brucella infection results in Type1 (Th1) cellular immune response which promotes a clearance of the bacterial organism. The development of this response is under the control of major cytokines like TNF-alpha, IFN-gamma and IL-12 produced at the onset of infection. We have observed that in humans, B. suis-infected macrophages which produce IL-1, IL-6, IL-10 and several chemokines including IL-8, do not secrete TNF-alpha. By constructing null mutants, we demonstrated that this inhibition involves the outer membrane protein Omp25 of Brucella, however the mechanism regulating the inhibition has not yet been clearly defined. It is likely that the Omp25-induced effect on TNF-alpha production assists bacterial evasion of antimicrobial defences at different levels. Firstly, by preventing the autocrine activation of macrophages thus inhibiting innate immunity and secondly by impairing the production of IL-12 and the development of a Th1 type specific immunity. In addition to the central role of the macrophage in Brucella infection, others cells of the innate immune response are recruited and influenced by the interactions between bacteria and host. For instance, human Vgamma9Vdelta2 T-cells play an important role in the early response to infection with intracellular pathogens. Evidence has been presented that their number dramatically increased in the peripheral blood of patients with acute brucellosis. We have shown that human Vgamma9Vdelta2 T-cells can be specifically activated by non-peptidic low molecular weight compound(s) from B. suis lysate or by soluble factors produced by B. suis-infected macrophages. Under these conditions, they produce TNF-alpha and IFN-gamma and reduce the bacterial multiplication inside infected autologous macrophages. This impairment of B. suis multiplication is due to both soluble factors released from activated gammadeltaT-cells (including TNF-alpha and IFN-gamma) and to a contact-dependent cytotoxicity directed against the infected cells. The interactions between the bacteria and these cells can counteract the intramacrophagic development of the bacteria and finally influence the further development of the host defense. We hypothesize that the chronicity or the elimination of the infection will depend on the balance between contradictory effects induced by the bacteria which favor either the host or the pathogen. Moreover, the interrelationship between the different cells must be taken into account in the analysis of the virulence of the bacteria and in the development of in vitro models of human macrophage infection.

Brucellosis in patients infected with the human immunodeficiency virus

Brucellosis has been described rarely in patients infected with HIV, despite the fact that eradication of intracellular brucellae is largely dependent on cell-mediated immunity. The characteristics of all patients with HIV infection and brucellosis seen in seven Spanish hospitals are reported. Since the beginning of the AIDS epidemic, 12 HIV-infected patients were diagnosed with brucellosis (8 with cultures positive for Brucella spp., 4 with high anti-Brucella antibody titers). Most patients were male and intravenous drug users. Eleven patients had no symptoms of HIV infection when first diagnosed with brucellosis and had relatively preserved cellular immunity (median CD4 + cell count 588, range 136-1006). There was a clear epidemiologic antecedent for acquisition of brucellosis in 11 patients. Clinical symptoms included fever, arthromyalgia, and sweating in all patients; four patients presented with focal disease. All patients had high agglutinin titers, and eight of nine had cultures positive for Brucella. Therapy with doxycycline and streptomycin was curative in all cases. Two patients experienced a recurrence of symptoms after initial treatment, although no microbiological relapses were documented after a median follow-up period of 18 months. HIV infection does not seem to increase the incidence of brucellosis. Since most cases occur in asymptomatic patients with relatively preserved immunity, the epidemiology, clinical presentation, diagnosis, response to therapy, and outcome are similar to those observed in non-HIV infected patients.