Immunology of Mycobacterium tuberculosis Infections

Tuberculosis (TB) is a serious global public health challenge that results in significant morbidity and mortality worldwide. TB is caused by infection with the bacilli Mycobacterium tuberculosis (M. tuberculosis), which has evolved a wide variety of strategies in order to thrive within its host. Understanding the complex interactions between M. tuberculosis and host immunity can inform the rational design of better TB vaccines and therapeutics. This chapter covers innate and adaptive immunity against M. tuberculosis infection, including insights on bacterial immune evasion and subversion garnered from animal models of infection and human studies. In addition, this chapter discusses the immunology of the TB granuloma, TB diagnostics, and TB comorbidities. Finally, this chapter provides a broad overview of the current TB vaccine pipeline.

Direct and Indirect Effects of Cytomegalovirus-Induced γδ T Cells after Kidney Transplantation

Despite effective anti-viral therapies, cytomegalovirus (CMV) is still associated with direct (CMV disease) and indirect effects (rejection and poor graft survival) in kidney transplant recipients. Recently, an unconventional T cell population (collectively designated as Vδ2^neg γδ T cells) has been characterized during the anti-CMV immune response in all solid-organ and bone-marrow transplant recipients, neonates, and healthy people. These CMV-induced Vδ2^neg γδ T cells undergo a dramatic and stable expansion after CMV infection, in a conventional “adaptive” manner. Similarly, as CMV-specific CD8+ αβ T cells, they exhibit an effector/memory TEMRA phenotype and cytotoxic effector functions. Activation of Vδ2^neg γδ T cells by CMV-infected cells involves the γδ T cell receptor (TCR) and still ill-defined co-stimulatory molecules such as LFA-1. A multiple of Vδ2^neg γδ TCR ligands are apparently recognized on CMV-infected cells, the first one identified being the major histocompatibility complex-related molecule endothelial protein C receptor. A singularity of CMV-induced Vδ2^neg γδ T cells is to acquire CD16 expression and to exert an antibody-dependent cell-mediated inhibition on CMV replication, which is controlled by a specific cytokine microenvironment. Beyond the well-demonstrated direct anti-CMV effect of Vδ2^neg γδ T cells, unexpected indirect effects of these cells have been also observed in the context of kidney transplantation. CMV-induced Vδ2^neg γδ T cells have been involved in surveillance of malignancy subsequent to long-term immunosuppression. Moreover, CMV-induced CD16+ γδ T cells are cell effectors of antibody-mediated rejection of kidney transplants, and represent a new physiopathological contribution to the well-known association between CMV infection and poor graft survival. All these basic and clinical studies paved the road to the development of a future γδ T cell-based immunotherapy. In the meantime, γδ T cell monitoring should prove a valuable immunological biomarker in the management of CMV infection.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.