TBX21

During a bout of influenza, B cells interact with other immune cells and then take different paths to defend the body. One path is the B cells that differentiate into lung-resident memory B cells, or lung-BRMs, that are critical for pulmonary immunity. These long-lived, non-circulating lung-BRMs migrate to the lungs from draining lymph nodes and reside there permanently as the first layer of defense that can quickly react to produce antibodies in a future infection. During a bout of influenza, B cells interact with other immune cells and then take different paths to defend the body. One path is the B cells that differentiate into antibody producing cells. Another path is the B cells that differentiate into lung-resident memory B cells, or lung-BRMs, that are critical for pulmonary immunity. Unlike antibody-producing B cells that help fight the current infection, the long-lived, non-circulating lung-BRMs migrate to the lungs from draining lymph nodes. They reside there permanently and lie in wait as the first layer of defense that can quickly react to produce antibodies in a future infection. Understanding the mechanism that creates these lung-BRMs is important for better flu vaccine development. Seasonal influenza kills 290,000 to 650,000 people each year, according to the World Health Organization. Yet flu vaccines are less effective in the elderly -- the most at-risk population -- compared to younger people. Also, there is need for vaccines that are more effective against later variants of a particular virus. André Ballesteros-Tato, Ph.D., and colleagues at the University of Alabama at Birmingham have now published a mouse-model study in the journal Immunity showing that interferon-gamma produced by T follicular helper cells, or Tfh cells, after intranasal influenza infection is required to initiate the path of B cell differentiation into lung-BRMs. Ballesteros-Tato is an associate professor in the UAB Department of Medicine Division of Clinical Immunology and Rheumatology. During influenza infection, both Tfh and B cells are present at germinal centers in the lymph nodes that drain the lungs. Class-switched memory B cells that are primed against the influenza virus begin to appear in the lungs at day 10 of the infection, and their numbers peak at Day 30. However, the UAB researchers found that, if mice were deficient in Tfh cells, or if the Tfh cells were blocked by an antibody, the lung-BRMs did not accumulate. Thus, Tfh cell help is required for class-switched-specific BRM responses to influenza. What role do the Tfh cells play? The UAB researchers found that the preferential differentiation of lung-BRMs early after infection correlated with differences in the Tfh cell response early in the viral infection. They found that the number of Tfh cells increased quickly and peaked between days 10 and 15. By Day 10, early in the flu infection, nearly 40 percent of the Tfh cells were producing interferon-gamma, or INF-γ; but that frequency dropped sharply thereafter. The production of INF-γ by Tfh cells turned out to be key to the lung-BRM response in flu. Ballesteros-Tato and colleagues found that mice whose Tfh cells were unable to produce INF-γ had a dramatically reduced frequency and number of influenza-specific BRMs in the lungs. Furthermore, the absence of INF-γ-producing Tfh cells, and therefore fewer lung-BRMs, was shown to compromise immune protection when mice were later reinfected with a different strain of influenza. The researchers asked whether the requirement for IFN-γ signaling in lung-BRM development was intrinsic to B cells, meaning the interferon was producing effects inside the B cells. They found that mice whose B cells lacked the receptor for INF-γ had significantly diminished numbers of flu-specific BRMs after influenza virus infection. Inside B cells, the transcription factor STAT1 is known to be required for optimal INF-γ signaling. The researchers found that mice whose B cells lacked STAT1 also failed to accumulate flu-specific BRMs after influenza infection. In mechanistic details, the researchers found that intrinsic IFN-γ-STAT1 signaling in B cells in the germinal center of lung-draining lymph nodes promoted expression of the T-bet transcription factor, and T-bet was necessary for differentiation into pre-memory B cells that express the surface marker CXCR3. Subsequently, CXCR3+ pre-memory B cells differentiated into CXCR3+ memory B cells, which exited the mediastinal lymph nodes and homed to the lung to become lung-BRMs. "In this proposed model, CXCR3+ memory B cells in the mediastinal lymph nodes are the precursors of lung-BRMs," said Ballesteros-Tato. "Our data provide evidence of a critical role for IFN-γ-producing Tfh cells in generating lung-BRM responses and provide new insights into the mechanisms that fine-tune germinal center B cell fate decisions after influenza virus infection." "This knowledge is essential for designing new vaccine strategies tailored to elicit potent lung-BRM responses, which have the potential to generate enhanced cross-protection to escape variants." Co-authors with Ballesteros-Tato in the study, "Interferon-γ production by Tfh cells is required for CXCR3+ pre-memory B cell differentiation and subsequent lung-resident memory B cell responses," are Nicole M. Arroyo-Díaz, Holly Bachus, Amber Papillion, Troy D. Randall and Jobaida Akther, UAB Department of Medicine, Division of Clinical Immunology and Rheumatology; and Alexander F. Rosenberg and Beatriz León, UAB Department of Microbiology. Support came from National Institutes of Health grants AI162698, AI150664, AI116584 and AI007051.

Memory B cells play a critical role to provide long-term immunity after a vaccination or infection. Researchers have now described a distinct and novel subset of memory B cells that predict long-lived antibody responses to influenza vaccination in humans. These effector memory B cells appear to be poised for a rapid serum antibody response upon secondary challenge one year later. Memory B cells play a critical role to provide long-term immunity after a vaccination or infection. In a study published in the journal Immunity, researchers describe a distinct and novel subset of memory B cells that predict long-lived antibody responses to influenza vaccination in humans. These effector memory B cells appear to be poised for a rapid serum antibody response upon secondary challenge one year later, Anoma Nellore, M.D., Fran Lund, Ph.D., and colleagues at the University of Alabama at Birmingham and Emory University report. Evidence from transcriptional and epigenetic profiling shows that the cells in this subset differ from all previously described memory B cell subsets. The UAB researchers identified the novel subset by the presence of FcRL5 receptor protein on the cell surface. In immunology, a profusion of different cell-surface markers is used to identify and separate immune-cell types. In the novel memory B cell subset, FcRL5 acts as a surrogate marker for positive expression of the T-bet transcription factor inside the cells. Various transcription factors act as master regulators to orchestrate the expression of many different gene sets as various cell types grow and differentiate. Nellore, Lund and colleagues found that the FcRL5+ T-bet+ memory B cells can be detected seven days after immunization, and the presence of these cells correlates with vaccine antibody responses months later. Thus, these cells may represent an early, easily monitored cellular compartment that can predict the development of a long-lived antibody response to vaccines. This could be a boon to the development of a more effective yearly influenza vaccine. "New annual influenza vaccines must be tested, and then manufactured, months in advance of the winter flu season," Lund said. "This means we must make an educated guess as to which flu strain will be circulating the next winter." Why are vaccine candidates made so far in advance? Pharmaceutical companies, Lund says, need to wait many weeks after vaccinating volunteers to learn whether the new vaccine elicits a durable immune response that will last for months. "One potential outcome of the current study is we may have identified a new way to predict influenza vaccine durability that would give us an answer in days, rather than weeks or months," Lund said. "If so, this type of early 'biomarker' could be used to test flu vaccines closer to flu season -- and moving that timeline might give us a better shot at predicting the right flu strain for the new annual vaccine." Seasonal flu kills 290,000 to 650,000 people each year, according to World Health Organization estimates. The global flu vaccine market was more than $5 billion in 2020. To understand the Immunity study, it is useful to remember what happens when a vaccinated person subsequently encounters a flu virus. Following exposure to previously encountered antigens, such as the hemagglutinin on inactivated influenza in flu vaccines, the immune system launches a recall response dominated by pre-existing memory B cells that can either produce new daughter cells or cells that can rapidly proliferate and differentiate into short-lived plasmablasts that produce antibodies to decrease morbidity and mortality. These latter B cells are called "effector" memory B cells. "The best vaccines induce the formation of long-lived plasma cells and memory B cells," said Lund, the Charles H. McCauley Professor in the UAB Department of Microbiology and director of the Immunology Institute. "Plasma cells live in your bone marrow and make protective antibodies that can be found in your blood, while memory B cells live for many years in your lymph nodes and in tissues like your lungs. "Although plasma cells can survive for decades after vaccines like the measles vaccine, other plasma cells wane much more quickly after vaccination, as is seen with COVID-19," Lund said. "If that happens, memory B cells become very important because these long-lived cells can rapidly respond to infection and can quickly begin making antibody." In the study, the UAB researchers looked at B cells isolated from blood of human volunteers who received flu vaccines over a span of three years, as well as B cells from tonsil tissue obtained after tonsillectomies. They compared naïve B cells, FcRL5+ T-bet+ hemagglutinin-specific memory B cells, FcRL5neg T-betneg hemagglutinin-specific memory B cells and antibody secreting B cells, using standard phenotype profiling and single-cell RNA sequencing. They found that the FcRL5+ T-bet+ hemagglutinin-specific memory B cells were transcriptionally similar to effector-like memory cells, while the FcRL5neg T-betneg hemagglutinin-specific memory B cells exhibited stem-like central memory properties. Antibody-secreting B cells need to produce a lot of energy to churn out antibody production, and they also must turn on processes that protect the cells from some of the detrimental side effects of that intense metabolism, including controlling the dangerous reactive oxygen species and boosting the unfolded protein response. The FcRL5+ T-bet+ hemagglutinin-specific memory B cells did not express the plasma cell commitment factor, but did express transcriptional, epigenetic and metabolic functional programs that poised these cells for antibody production. These included upregulated genes for energy-intensive metabolic processes and cellular stress responses. Accordingly, FcRL5+ T-bet+ hemagglutinin-specific memory B cells at Day 7 post-vaccination expressed intracellular immunoglobulin, a sign of early transition to antibody-secreting cells. Furthermore, human tonsil-derived FcRL5+ T-bet+ memory B differentiated more rapidly into antibody-secreting cells in vitro than did FcRL5neg T-betneg hemagglutinin-specific memory B cells. Lund and Nellore, an associate professor in the UAB Department of Medicine Division of Infectious Diseases, are co-corresponding authors of the study, "A transcriptionally distinct subset of influenza-specific effector memory B cells predicts long-lived antibody responses to vaccination in humans." Co-authors with Lund and Nellore are Esther Zumaquero, R. Glenn King, Betty Mousseau, Fen Zhou and Alexander F. Rosenberg, UAB Department of Microbiology; Christopher D. Scharer, Tian Mi, Jeremy M. Boss, Christopher M. Tipton and Ignacio Sanz, Emory University School of Medicine, Atlanta, Georgia; Christopher F. Fucile, UAB Informatics Institute; John E. Bradley and Troy D. Randall, UAB Department of Medicine, Division of Clinical Immunology and Rheumatology; and Stuti Mutneja and Paul A. Goepfert, UAB Department of Medicine Division of Infectious Diseases. Funding for the work came from National Institutes of Health grants AI125180, AI109962 and AI142737 and from the UAB Center for Clinical and Translational Science.