Mycobacterium tuberculosis (Mtb) infection is initiated in the distal airways, but the bacteria ultimately disseminate to the lung interstitium. Although various cell types, including alveolar macrophages (AM), neutrophils, and permissive monocytes, are known to be infected with Mtb, the initially infected cells as well as those that mediate dissemination from the alveoli to the lung interstitium are unknown. In this study, using a murine infection model, we reveal that early, productive Mtb infection occurs almost exclusively within airway-resident AM. Thereafter Mtb-infected, but not uninfected, AM localize to the lung interstitium through mechanisms requiring an intact Mtb ESX-1 secretion system. Relocalization of infected AM precedes Mtb uptake by recruited monocyte-derived macrophages and neutrophils. This dissemination process is driven by non-hematopoietic host MyD88/interleukin-1 receptor inflammasome signaling. Thus, interleukin-1-mediated crosstalk between Mtb-infected AM and non-hematopoietic cells promotes pulmonary Mtb infection by enabling infected cells to disseminate from the alveoli to the lung interstitium.

Worldwide rates of systemic fungal infections, including three of the major pathogens responsible for such infections in North America (Coccidioides posadasii, Histoplasma capsulatum, and Blastomyces dermatitidis), have soared recently, spurring interest in developing vaccines. The development of Th1 cells is believed to be crucial for protective immunity against pathogenic fungi, whereas the role of Th17 cells is vigorously debated. In models of primary fungal infection, some studies have shown that Th17 cells mediate resistance, while others have shown that they promote disease pathology. Here, we have shown that Th1 immunity is dispensable and that fungus-specific Th17 cells are sufficient for vaccine-induced protection against lethal pulmonary infection with B. dermatitidis in mice. Further, vaccine-induced Th17 cells were necessary and sufficient to protect against the three major systemic mycoses in North America. Mechanistically, Th17 cells engendered protection by recruiting and activating neutrophils and macrophages to the alveolar space, while the induction of Th17 cells and acquisition of vaccine immunity unexpectedly required the adapter molecule Myd88 but not the fungal pathogen recognition receptor Dectin-1. These data suggest that human vaccines against systemic fungal infections should be designed to induce Th17 cells if they are to be effective.

Highlights d CytoMAP is a user-friendly, comprehensive platform for spatial analysis of tissues d Allows quantification of cellular positioning and global tissue structure d Enables exploration of cellular and tissue microenvironment heterogeneity d CytoMAP reveals fundamental features of myeloid cell organization in lymph nodes

Dimorphic fungi collectively account for 5 to 10 million new infections annually worldwide. Ongoing efforts seek to clarify mechanisms of cellular resistance to these agents and develop vaccines. A major limitation in studying the development of protective T-cells in this group of organisms is the lack of tools to detect, enumerate and characterize fungus-specific T-cells during vaccination and infection. We generated a TCR transgenic (tg) mouse (Bd 1807) whose CD4+ T cells respond to a native epitope in Blastomyces dermatitidis and also in Histoplasma capsulatum. Here, we characterize the mouse, reveal its applications, and extend our analysis showing that 1807 cells also respond to the related dimorphic fungi Coccidioides posadasii and Paracoccidioides lutzii. On adoptive transfer into vaccinated wild-type mice, 1807 cells become activated, proliferate and expand in the draining lymph nodes, and differentiate into T1 effectors after trafficking to the lung upon lethal experimental challenge. 1807 cells confer vaccine-induced resistance against B. dermatitidis, H. capsulatum and C. posadasii. Transfer of naïve 1807 cells at serial intervals post-vaccination uncovered the prolonged duration of fungal Ag presentation. Using 1807 cells, we also found that the administration of vaccine only once induced a maximal pool of effector/memory CD4+ cells and protective immunity by four weeks after vaccination. The autologous adoptive transfer system described here reveals novel features of anti-fungal immunity and offers a powerful approach to study the differentiation of Ag-specific T cells responsive to multiple dimorphic fungi and the development of CD4+ T-cell memory needed to protect against fungal infection.

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Growing evidence suggests the outcome of Mycobacterium tuberculosis infection is established rapidly after exposure, but how the current tuberculosis vaccine, bacillus Calmette–Guérin (BCG), impacts early immunity is poorly understood. In this study, we found that murine BCG immunization promotes a dramatic shift in infected cell types. Although alveolar macrophages are the major infected cell for the first 2 weeks in unimmunized animals, BCG promotes the accelerated recruitment and infection of lung-infiltrating phagocytes. Interestingly, this shift is dependent on CD4 T cells, yet does not require intrinsic recognition of Ag presented by infected alveolar macrophages. M. tuberculosis–specific T cells are first activated in lung regions devoid of infected cells, and these events precede vaccine-induced reduction of the bacterial burden, which occurs only after the colocalization of T cells and infected cells. Understanding how BCG alters early immune responses to M. tuberculosis provides new avenues to improve upon the immunity it confers.