Adult human lungs inhale ~11,000 liters of air daily and are a direct interface between the systemic circulation and external environment. For this reason, the lungs play a critical role in the immune defense against inspired pathogens to ensure maintenance of gas exchange, while protecting the host. These responses integrate both the innate and adaptive arms tailored to the lung environment. Recent data has shown that healthy adult human lungs harbor distinct subsets of tissue resident memory CD4 TRM, CD8 TRM, BRM, and antibody secreting cells as integral components to immunity against respiratory pathogens; all aspects that have been successfully modeled in mice and involve cross talk with the local microenvironment. T cell immunity needs antigen presentation by monocytes and epithelial cells for establishing lung residency, while requiring help from epithelial and fibroblast cells to recruit antimicrobial neutrophils. Further, fibroblasts and stromal cells secrete soluble factors that may play key roles in maintaining the tertiary lymphoid structures within the lungs. Single cell sequencing is revealing an unforeseen heterogeneity in lung cell types and a more careful delineation of different adaptive-immune supportive functions for known and novel lung cell types with a greater resolution is warranted.
Although some aspects of how lung T and B cells confer protection are described, many other mechanisms remain undelineated and whether different subsets of lung T and B cells perform discrete non-overlapping functions is unclear. There is increasing evidence that vigorous adaptive antimicrobial responses can incite severe lung damage. The cellular and molecular factor/s aggravating or optimizing this delicate balance between protection and pathology need defining. Given the worsened outcomes of respiratory infections in the aged (arguably carrying more immune memory as a consequence of years lived), the factor/s leading to waning T and B cell immunity in the aged are uncertain. Whether aged hosts (naïve or previously immunized) respond to new infection or vaccinations with a comparable quantity and quality of immunity as younger counterparts is also understudied. Further, whether “original antigenic sin” (the loss of our ability to respond to new variants because of existing immunity to immunodominant epitopes) extends to T cell responses is unknown. All these topics highlight the gaps in our fundamental knowledge of lung immunity to pathogens that need
attention.
The ongoing pandemic has exposed several gaps in our knowledge about the design and mechanism of vaccines against respiratory pathogens. The new generation of mRNA vaccines induce strong protection against rapidly mutating virus, though the mechanisms leading to superior immunity are unclear. Alternative mucosal vaccine strategies induce robust local responses, including lung TRM and BRM cells. Studies elucidating effectiveness of these strategies in driving prompt frontline immunity are in its nascence. Vaccine designs with strong adjuvanticity (e.g. liposomes and RNA molecules) and focused on T cell responses that target internal conserved proteins of viruses are potent for sustained protection against rapidly mutating viruses. If and how local lung cells can be reprogrammed to support these vaccine-induced T (and B) cells is an emerging area that warrants more investigation. Finally, a major hurdle to combating respiratory infections is our inability to induce sustained long-term protection via vaccines. Although total antibody responses wane, memory B cells evolve and increase in frequency over time. Then, the reasons for immunity weakening over time is unclear. The waning of T cell immunity, particularly the “quality” of the memory T cell response, long after vaccination is also less studied.
For this issue, “Adaptive Immunity to Respiratory Pathogens”, we welcome submissions of manuscripts on any topics discussed above and mentioned below:
(1) Roles of innate immunity in influencing adaptive immunity to respiratory pathogens: roles of respiratory tract epithelial cells, lung structural cells (including, but not limited to, known and novel subsets of fibroblasts, vascular endothelial, lymphatic endothelial, mesenchymal cells) in influencing adaptive immunity
(2) Pathogenic impacts of potent innate and adaptive immune responses in the lung
(3) Maladaptive remodeling of lungs post recovery from respiratory infections
(4) Waning of vaccine- or infection-induced T- and B-cell immunity across the young and aged. How can we extend their stability?
(5) Vaccine design: targeting T- and B-cell responses and supporting cells, adjuvants and immunization routes
(6) Why are the aged disproportionately impacted by respiratory infections?
(7) Impact of repeated vaccine boosting on quality of immune responses
Adult human lungs inhale ~11,000 liters of air daily and are a direct interface between the systemic circulation and external environment. For this reason, the lungs play a critical role in the immune defense against inspired pathogens to ensure maintenance of gas exchange, while protecting the host. These responses integrate both the innate and adaptive arms tailored to the lung environment. Recent data has shown that healthy adult human lungs harbor distinct subsets of tissue resident memory CD4 TRM, CD8 TRM, BRM, and antibody secreting cells as integral components to immunity against respiratory pathogens; all aspects that have been successfully modeled in mice and involve cross talk with the local microenvironment. T cell immunity needs antigen presentation by monocytes and epithelial cells for establishing lung residency, while requiring help from epithelial and fibroblast cells to recruit antimicrobial neutrophils. Further, fibroblasts and stromal cells secrete soluble factors that may play key roles in maintaining the tertiary lymphoid structures within the lungs. Single cell sequencing is revealing an unforeseen heterogeneity in lung cell types and a more careful delineation of different adaptive-immune supportive functions for known and novel lung cell types with a greater resolution is warranted.
Although some aspects of how lung T and B cells confer protection are described, many other mechanisms remain undelineated and whether different subsets of lung T and B cells perform discrete non-overlapping functions is unclear. There is increasing evidence that vigorous adaptive antimicrobial responses can incite severe lung damage. The cellular and molecular factor/s aggravating or optimizing this delicate balance between protection and pathology need defining. Given the worsened outcomes of respiratory infections in the aged (arguably carrying more immune memory as a consequence of years lived), the factor/s leading to waning T and B cell immunity in the aged are uncertain. Whether aged hosts (naïve or previously immunized) respond to new infection or vaccinations with a comparable quantity and quality of immunity as younger counterparts is also understudied. Further, whether “original antigenic sin” (the loss of our ability to respond to new variants because of existing immunity to immunodominant epitopes) extends to T cell responses is unknown. All these topics highlight the gaps in our fundamental knowledge of lung immunity to pathogens that need
attention.
The ongoing pandemic has exposed several gaps in our knowledge about the design and mechanism of vaccines against respiratory pathogens. The new generation of mRNA vaccines induce strong protection against rapidly mutating virus, though the mechanisms leading to superior immunity are unclear. Alternative mucosal vaccine strategies induce robust local responses, including lung TRM and BRM cells. Studies elucidating effectiveness of these strategies in driving prompt frontline immunity are in its nascence. Vaccine designs with strong adjuvanticity (e.g. liposomes and RNA molecules) and focused on T cell responses that target internal conserved proteins of viruses are potent for sustained protection against rapidly mutating viruses. If and how local lung cells can be reprogrammed to support these vaccine-induced T (and B) cells is an emerging area that warrants more investigation. Finally, a major hurdle to combating respiratory infections is our inability to induce sustained long-term protection via vaccines. Although total antibody responses wane, memory B cells evolve and increase in frequency over time. Then, the reasons for immunity weakening over time is unclear. The waning of T cell immunity, particularly the “quality” of the memory T cell response, long after vaccination is also less studied.
For this issue, “Adaptive Immunity to Respiratory Pathogens”, we welcome submissions of manuscripts on any topics discussed above and mentioned below:
(1) Roles of innate immunity in influencing adaptive immunity to respiratory pathogens: roles of respiratory tract epithelial cells, lung structural cells (including, but not limited to, known and novel subsets of fibroblasts, vascular endothelial, lymphatic endothelial, mesenchymal cells) in influencing adaptive immunity
(2) Pathogenic impacts of potent innate and adaptive immune responses in the lung
(3) Maladaptive remodeling of lungs post recovery from respiratory infections
(4) Waning of vaccine- or infection-induced T- and B-cell immunity across the young and aged. How can we extend their stability?
(5) Vaccine design: targeting T- and B-cell responses and supporting cells, adjuvants and immunization routes
(6) Why are the aged disproportionately impacted by respiratory infections?
(7) Impact of repeated vaccine boosting on quality of immune responses
