Martin E. Rottenberg

Expression patterns of NKG2A, KIR, and CD57 define a process of CD56dim NK cell differentiation uncoupled from NK cell education

Natural killer (NK) cells are lymphocytes of the innate immune system that, following differentiation from CD56(bright) to CD56(dim) cells, have been thought to retain fixed functional and phenotypic properties throughout their lifespan. In contrast to this notion, we here show that CD56(dim) NK cells continue to differentiate. During this process, they lose expression of NKG2A, sequentially acquire inhibitory killer cell inhibitory immunoglobulin-like receptors and CD57, change their expression patterns of homing molecules, and display a gradual decline in proliferative capacity. All cellular intermediates of this process are represented in varying proportions at steady state and appear, over time, during the reconstitution of the immune system, as demonstrated in humanized mice and in patients undergoing hematopoietic stem cell transplantation. CD56(dim) NK-cell differentiation, and the associated functional imprint, occurs independently of NK-cell education by interactions with self-human leukocyte antigen class I ligands and is an essential part of the formation of human NK-cell repertoires.

Tuberculosis and HIV Co-Infection

Tuberculosis (TB) and HIV co-infections place an immense burden on health care systems and pose particular diagnostic and therapeutic challenges. Infection with HIV is the most powerful known risk factor predisposing for Mycobacterium tuberculosis infection and progression to active disease, which increases the risk of latent TB reactivation 20-fold. TB is also the most common cause of AIDS-related death. Thus, M. tuberculosis and HIV act in synergy, accelerating the decline of immunological functions and leading to subsequent death if untreated. The mechanisms behind the breakdown of the immune defense of the co-infected individual are not well known. The aim of this review is to highlight immunological events that may accelerate the development of one of the two diseases in the presence of the co-infecting organism. We also review possible animal models for studies of the interaction of the two pathogens, and describe gaps in knowledge and needs for future studies to develop preventive measures against the two diseases.

Neutrophil secretion products pave the way for inflammatory monocytes

The leukocyte response in inflammation is characterized by an initial recruitment of polymorphonuclear leukocytes (PMN) preceding a second wave of monocytes to the site of injury or infection. In the mouse, 2 populations of monocytes have been identified, Gr1(-)CCR2(-)CX3CR1(hi) resident monocytes and Gr1(+)CCR2(+)CX3CR1(lo) inflammatory monocytes. Here, intravital microscopy of the musculus cremaster and a subcutaneous air pouch model were used to investigate a possible link between PMN extravasation and the subsequent emigration of inflammatory monocytes in response to local stimulation with PAF. In mice that were made neutropenic by injection of a PMN-depleting antibody, the extravasation of inflammatory monocytes, but not resident monocytes, was markedly reduced compared with mice with intact white blood cell count but was restored by local treatment with secretion of activated PMN. Components of the PMN secretion were found to directly activate inflammatory monocytes and further examination revealed PMN-derived LL-37 and heparin-binding protein (HBP/CAP37/azurocidin) as primary mediators of the recruitment of inflammatory monocytes via activation of formyl-peptide receptors. These data show that LL-37 and HBP specifically stimulate mobilization of inflammatory monocytes. This cellular cross-talk functionally results in enhanced cytokine levels and increased bacterial clearance, thus boosting the early immune response.

The role of IFN-γ in the outcome of chlamydial infection

Chlamydia are intracellular bacteria which infect many vertebrates, including humans. They cause a myriad of severe diseases, ranging from asymptomatic infection to pneumonia, blindness or infertility. IFN-gamma plays an important role in defense against acute infection and in the establishment of persistence. Chlamydia have evolved mechanisms to escape IFN-gamma functions. IFN-gamma-mediated effector mechanisms may involve effects on the metabolism of tryptophan or iron, on the inducible NO synthase (iNOS), on the secretion of chemokines and adhesion molecules or on the regulation of T-cell activities. IFN-gamma is secreted by the innate and the adaptive arms of the immune system. Within the former, Chlamydia-infected macrophages express IFN-gamma that in turn mediates resistance to infection. IFN-alpha/beta are pivotal for both IFN-gamma- and iNOS-mediated resistance to chlamydial infection in macrophages.

Bcl-2, Bax and p53 expression in B-CLL in relation to in vitro survival and clinical progression.

Our previous data have shown that isolated leukemic cells from progressive chronic lymphocytic leukemia (B‐CLL) patients respond to growth stimulation in vitro and express high levels of p53, immunoreactive with the configuration‐specific antibody PAb 240. We have now analyzed the in vitro survival of B‐CLL cells in relation to Bcl‐2, Baxα and p53 expression and compared this with the clinical progression of the disease. Leukemic cells from patients with progressive disease demonstrated higher in vitro survival, compared with non‐progressive B‐CLL and normal B cells. All cells were sensitive to treatment with a combination of glucocorticoid and cAMP. Bcl‐2 protein levels were not related to clinical progression, as measured by flow cytometry. Competitive PCR showed that Bcl‐2 mRNA was over‐expressed in most of the B‐CLL samples and that p53 mRNA expression was similar between B‐CLL groups and normal values and thus not related to clinical progression. However, since Baxα expression was lower in progressive than in non‐progressive patients, the Bcl‐2/Baxα ratio at the mRNA level was significantly higher in the progressive group. Our data suggest that the Bcl‐2/Baxα ratio is important for the regulation of B‐CLL cell survival, that p53 over‐expression in progressive B‐CLL is the result of post‐transcriptional modifications and that a directed PKA activation may potentiate the cytolytic effect of glucocorticoids in vivo.

Regulation and Role of IFN-γ in the Innate Resistance to Infection with Chlamydia pneumoniae

By using mice genomically lacking IFN-γR, IL-12, perforin, and recombination-activating gene-1 (RAG-1), we analyzed the regulation and importance of IFN-γ in the control of infection with Chlamydia pneumoniae. IL-12 participates in resistance of mice to C. pneumoniae, probably by regulating the protective levels of IFN-γ mRNA. In turn, IFN-γ is necessary for the increased IL-12p40 mRNA accumulation that occurs in lungs during infection with C. pneumoniae, suggesting a positive feedback regulation between these two cytokines. In experiments including RAG-1−/−/IFN-γR−/− mice we showed that IFN-γ produced by innate cells controls the bacterial load and is necessary for the increased accumulation of transcripts for enzymes controlling high output NO release (inducible NO synthase), superoxide production (gp-91 NADPH oxidase), and catalyzis of tryptophan (indoleamine 2,3-dioxygenase (IDO)), mechanisms probably related to bacterial killing. Adaptive immune reponses diminish the levels of IFN-γ and IL-12 mRNA and thereby the levels of inducible NO synthase, IDO, and gp91 NADPH oxidase trancripts. By using RAG-1−/−/perforin−/− mice, we excluded the overt participation of NK cell cytotoxicity in the control of C. pneumoniae. However, NK cells and probably other innate immune cells release IFN-γ during the bacterial infection.

IFN-αβ-Dependent, IFN-γ Secretion by Bone Marrow-Derived Macrophages Controls an Intracellular Bacterial Infection

Several reports have indicated that cell lineages apart from NK and T cells can also express IFN-γ. However, the biological relevance of this finding is uncertain. We show in this study that bone marrow-derived macrophages (BMMs) express IFN-γ at the mRNA and protein level early after infection with Chlamydia pneumoniae. Increased IFN-γ mRNA accumulation by infected BMMs is early, transient, and requires both bacterial and host protein synthesis. The induction of IFN-γ mRNA levels is independent of IL-12 and was dramatically enhanced in IL-10−/− BMMs. Such IL-10−/− BMMs contained less bacteria than the wild-type controls, whereas IFN-γR−/− BMMs showed increased C. pneumoniae load. Inducible NO synthase (iNOS) also participates in the control of bacterial load, as shown by the enhanced numbers of C. pneumoniae in iNOS−/− BMMs. However, the increased accumulation of iNOS mRNA and NO in C. pneumoniae-infected BMMs depended on the presence of IFN-αβ, but was independent of IFN-γ. Interestingly, IFN-αβ are also required for increased IFN-γ mRNA accumulation in C. pneumoniae-infected BMMs. Accordingly, IFN-αβR−/− BMMs showed higher levels of C. pneumoniae than wild-type BMMs. Our findings unravel an autocrine/paracrine macrophage activation pathway by showing an IFN-αβ-dependent IFN-γ and iNOS induction in response to infection, which protects macrophages against intracellular bacterial growth.

Chlamydia pneumoniae Infection Does Not Induce or Modify Atherosclerosis in Mice

Background—Seroepidemiological studies have linked Chlamydia pneumoniae (CP) to coronary heart disease, and recent experimental studies suggest that it may accelerate or even induce atherosclerosis. We therefore evaluated the effect of CP infection on atherosclerosis in atherosclerosis-prone apolipoprotein E-knockout (apoE-KO) and wild-type C57BL/6J mice. Methods and Results—Six- to 8-week-old female mice were infected intranasally with live CP and then fed a standard chow diet for 22 weeks. A subgroup of mice was reinfected 18 weeks after primary infection. Polymerase chain reaction analysis of lung tissue confirmed successful infection with CP, and ELISA assays demonstrated development of a humoral immune response. Despite this, no statistically significant differences in aortic atherosclerotic lesions were found between CP-infected and control apoE-KO mice. Furthermore, CP infection did not induce atherosclerosis in C57BL/6J mice. Conclusions—CP does not induce atherosclerosis in wild-type mice and does not accelerate atherosclerosis in chow-fed apoE-KO mice. Further studies will be necessary to clarify the explanation for the seroepidemiological association between CP and coronary heart disease in humans.

Cerebral vessel laminins and IFN-γ define Trypanosoma brucei brucei penetration of the blood-brain barrier

Subspecies of Trypanosoma brucei cause severe brain diseases after penetration of the blood-brain barrier. We investigated whether cytokines that modulate inflammatory cell infiltration into the brain also influence T. brucei neuroinvasion. Migration of a rodent pathogenic T. brucei strain from the cerebral blood vessels into the brain parenchyma was impeded in IFN-gamma(-/-), IFN-gamma receptor(-/-) (IFN-gammaR(-/-)), IL-12p40(-/-), and recombinant activating gene-1(-/-) (RAG-1(-/-)) mice as compared with their WT littermates despite higher levels of parasitemia in the mutant strains. Parasites accumulated in the perivascular compartment, confined between the endothelial and the parenchymal basement membranes, in certain areas of the brains of IFN-gamma(-/-), IFN-gammaR(-/-), and RAG-1(-/-) mice. This accumulation occurred around endothelial basement membranes containing the laminin alpha4 chain, while blood vessels showing robust laminin alpha5 chain immunostaining were not associated with parasite infiltration. The number of CD4+ and CD8+ T cells infiltrating the brain parenchyma was also reduced in the IFN-gamma(-/-) and IFN-gammaR(-/-) mice. Our findings suggest that lymphocyte-derived IFN-gamma facilitates trypanosome penetration across cerebral blood vessels and that the site of penetration is determined by the composition of the basement membranes of these vessels.

SOCS3, a major regulator of infection and inflammation

In this review, we describe the role of suppressor of cytokine signaling-3 (SOCS3) in modulating the outcome of infections and autoimmune diseases as well as the underlying mechanisms. SOCS3 regulates cytokine or hormone signaling usually preventing, but in some cases aggravating, a variety of diseases. A main role of SOCS3 results from its binding to both the JAK kinase and the cytokine receptor, which results in the inhibition of STAT3 activation. Available data also indicate that SOCS3 can regulate signaling via other STATs than STAT3 and also controls cellular pathways unrelated to STAT activation. SOCS3 might either act directly by hampering JAK activation or by mediating the ubiquitination and subsequent proteasome degradation of the cytokine/growth factor/hormone receptor. Inflammation and infection stimulate SOCS3 expression in different myeloid and lymphoid cell populations as well as in diverse non-hematopoietic cells. The accumulated data suggest a relevant program coordinated by SOCS3 in different cell populations, devoted to the control of immune homeostasis in physiological and pathological conditions such as infection and autoimmunity.