UAB Identifies Six Novel Subsets, Reshaping Immune Knowledge

At first glance, the immune response to a flu virus seems straightforward. Some cells detect the infection and alert the immune system. In turn, the immune system produces antibodies to fight the virus. Antigen enters, antibody exits.

However, over the past 65 years, researchers have found that the steps between detection and antibody production are far more complex. Specific cells present the flu antigen to the immune system. In response, certain immune cells interact directly to trigger a defense. B cells, which are responsible for making antibodies, undergo numerous genetic mutations to generate a diverse range of antibodies.

These cells switch between different antibody types, such as IgM and IgG. B cells that produce ineffective antibodies are eliminated, while those that produce effective antibodies increase their metabolic activity to produce large amounts of antibody protein.

The memory immune response to flu, though less understood, is equally complex. It involves creating memory cells that remain in the lungs and lymph nodes. These cells do not produce antibodies immediately. Instead, they stay dormant, ready to activate quickly and generate antibodies upon re-exposure to the virus.

Fran Lund, Ph.D., a professor of microbiology and head of the University of Alabama at Birmingham Immunology Institute, and her colleagues identified six subsets of memory B cells in a study published in Immunity. One of these subsets produces the transcription factor T-bet.

Through genetic analysis and targeted modifications, the researchers showed that continuous T-bet expression is required to maintain these memory B cells. In a rat flu model, they found that memory B cells in the lungs and lymph nodes needed T-bet to survive. These cells were also capable of rapidly turning into antibody-secreting plasma cells.

T-bet is a transcription factor—a protein in the cell nucleus that can switch specific genes on or off. Groups of transcription factors work together to regulate genes that control how cells function and develop.

Previous studies have shown that T-bet expression is linked to key traits of human vaccine-specific memory B cells. It’s also associated with long-lasting immune responses in mouse germinal center B cells after viral infection.

To investigate further, UAB researchers infected mice with the flu virus. Thirty days later, they isolated mature memory B cells that responded to the influenza NP antigen. They then used single-cell sequencing to analyze gene expression in each cell. The results were grouped into seven distinct clusters.

One cluster was excluded due to differences in development. The remaining six clusters were analyzed for transcription factors, B-cell receptor patterns, and gene expression profiles. Cluster 2 stood out. It had high levels of T-bet and genes also found in human effector memory B cells after flu vaccination.

In cluster 2, elevated protein synthesis genes suggested these cells were shifting from a memory state to an antibody-producing state. While cluster 2 showed traits of effector memory B cells, the other clusters showed features related to stem-like function, tissue surveillance, or inflammation.

To confirm T-bet’s role, researchers deleted the T-bet gene from B cells, either permanently or temporarily. They found that T-bet marks memory B cells in the lungs and lymph nodes that can rapidly become antibody-producing cells. Without T-bet, lung memory B cells failed to launch a secondary antibody response after reinfection.

Looking ahead, the researchers hope to use these insights to develop new strategies that boost T-bet expression in human memory B cells. This could help create immune cells that stay at infection sites and provide faster protection against the flu.