Pneumonia is a lung infection causing air sacs to fill with fluid such that breathing becomes impaired. Although some forms of pneumonia are viral, most pneumonia is caused by the bacterium Streptococcus pneumoniae. Interestingly, while this bacterium can live harmlessly in the nose and throat, it can cause disease in immune-compromised individuals, babies, or the elderly. S. pneumoniae is in fact the most common cause of community-acquired pneumonia and meningitis in the elderly. The CDC reports that 1.3 million Americans go to the emergency room each year due to pneumonia. In 2017, 49,157 of these patients died. 

While available vaccines and antibiotics have decreased pneumococcal infections overall,  several strains of antibiotic-resistant S. pneumoniae have emerged, emphasizing the need for improved vaccines and treatments. Researchers and doctors also need to know how S. pneumoniae transforms from a peaceful member of our body’s ecosystem to an invasive and lethal pathogen.

Our Approach

LJI immunologist Mitchell Kronenberg, Ph.D., leads efforts to understand how healthy individuals contain infection by bacteria such S. pneumoniae. His team focuses on specialized populations of lymphocytes that make very rapid or innate-like immune responses against the pathogen. They found that when S. pneumoniae invades the lung, immune cells called invariant natural killer T (iNKT) cells mount an immediate and highly choreographed immune response that prevents the infection from progressing. Moreover, since iNKT cells in different patients appear to target S. pneumoniae in the same way  (unlike other types of T cells) scientists may someday be able to reliably activate them to fight pneumonia in newly infected patients.

Kronenberg’s team is using mouse models and cutting-edge intravital microscopy to follow iNKT cell mobilization in living animals after S. pneumoniae infection. Their research charts how different subsets of iNKT cells emerge following infection, each secreting different chemical messenger (cytokine) signals at the “right” time. We now know that iNKT cell subsets can only neutralize lung infections if they are activated in a certain order in the right part of the airway. Researchers can build upon these findings to design potent pneumonia vaccines.


Jul 8, 2020
Kronenberg Lab

Mitchell Kronenberg, Ph.D., and his team study T cells – white blood cells responsible for recognizing and responding to foreign invaders, such as microbes.

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Mitchell Kronenberg, Ph.D.
Professor, President Emeritus
Center for Autoimmunity and Inflammation, Center for Infectious Disease and Vaccine Research