Published August 21, 2020
Researchers exploring the nature of immunity after vaccination against Streptococcus pneumoniae have discovered that a specific type of white blood cell called neutrophils plays a more critical role than was previously known.
This research is especially relevant for the elderly because immunity declines with age.
The preclinical study is important because it is the first to use Prevnar-13, one of two pneumonia vaccines on the market, instead of a model antigen to study the nature of the immune response triggered by the vaccine.
While B cells are a key factor in the immune response because they produce antibodies that fight pathogens, Bou Ghanem says the new findings about neutrophils could be relevant to potential improvements in developing vaccines against S. pneumoniae.
“Now we have to think about the other immune cells in the mix as well,” she says. “Now we understand that it’s a little more complicated.”
The researchers have found that in order to generate a protective response when vaccinated against Streptococcus pneumoniae, the host must have a sufficient level of neutrophils.
Bou Ghanem describes neutrophils as “the first defenders,” noting that “whenever any foreign object appears in the lungs, neutrophils are the first infection-fighting cells to appear.”
That fact has long been known about neutrophils, also known as polymorphonuclear leukocytes (PMNs). They play key roles in the body’s rapid response to bacterial infection, known as the innate response.
But the researchers found that they also play a role in generating the adaptive response, the immune system’s slower, more customized response to a specific infection.
“We have learned now that neutrophils orchestrate the whole immune response, both innate and adaptive,” says Essi Yayra Ines Tchalla, first author on the paper and a doctoral student in the Department of Microbiology and Immunology.
They made the discovery while studying how two groups of mice responded after being vaccinated with the polysaccharide conjugate vaccine: One group was normal and one group had had its neutrophils significantly depleted.
When infected with S. pneumoniae a month after vaccination, all of the mice with normal neutrophil levels were able to mount a strong immune response and all of them survived, with only 12.5 percent of them showing any symptoms.
But in the group that had been depleted of neutrophils at the time of vaccination, nearly 80 percent became severely ill and more than half of the mice did not survive. These mice exhibited between 10 and 100 times more bacteria in their lungs than was seen in the normal controls.
The researchers report it was the lack of neutrophils at the time when mice were vaccinated, not at the time of exposure to the bacteria, that caused them to suffer the worst outcomes. The neutrophils were required for the production of protective antibodies against S. pneumoniae following vaccination.
“Now we want to figure out what is the contribution of neutrophils in regulating this vaccine response,” Tchalla says.
She explains that the team is looking at the possibility that neutrophils can produce a cytokine called interferon gamma, which in turn helps B cells to produce better antibodies against pathogens.
The long-range goal for Bou Ghanem and Tchalla is to investigate how the reduction in the efficacy of neutrophils in the elderly affects their ability to mount an immune response to S. pneumoniae when vaccinated.
One of their projects, currently on hold because of the pandemic, involves studying neutrophils provided by young and senior donors recruited through UB’s Clinical and Translational Science Institute, a collaboration with Sanjay Sethi, MD, professor of medicine and chief of the Division of Pulmonary, Critical Care and Sleep Medicine.
The findings may also be relevant to understanding the ability of elderly patients to generate an adequate immune response when vaccinated against other pathogens, including COVID-19, the researchers say.
The research — published in May in the Journal of Infectious Diseases — was funded by the National Institutes of Health. Bou Ghanem has received additional NIH funding to study the factors that make the elderly susceptible to S. pneumoniae, and how to make vaccines more effective in elderly populations, in collaboration with Blaine Pfeifer, PhD, professor in the School of Engineering and Applied Sciences.
In addition to Bou Ghanem and Tchalla, co-authors are: