"With SARS-CoV-2, a virus no one had ever encountered before, we saw that people in their 50s and 60s were very susceptible to severe COVID, but most kids exposed to SARS-CoV-2 were fine, and many didn't even have symptoms," Farber says. It also may explain why young kids are more resilient to new respiratory infections compared to adults - including SARS-CoV-2. "This mechanism helps young children respond to the many different respiratory pathogens they encounter early in life." "BALT enables the lung to make antibodies to respiratory pathogens well before T cell memory has developed but fall apart in later childhood when they are no longer needed," says Farber. This bronchus-associated lymphoid tissue, or BALT, is formed between 6 and 12 months of age and disappears after age 3. The researchers found clusters of antibody-producing B cells surrounded by T cells in the infants' lungs.
'Secret weapon' protects babies from new pathogensīut while babies are highly susceptible to recurrent infections, a second study, published in Nature Immunology, found that babies have a unique way of coping with new pathogens. "Early memory T cells are more tolerant than mature memory cells, so they're not going to create an immune response against new foods," Farber says.
The findings also may explain why introducing foods to children during the first year of life could prevent severe food allergies. "This explains why babies and young children are more vulnerable to recurrent respiratory infections and other infectious diseases compared with adults." "We found that memory T cells in young children are not functionally mature and only begin to have the capacity for protective immunity at around ages 4 to 6 years," Farber says. These cells enable older children and adults to mount an immediate and specific immune response during the next encounter with a pathogen.
One study, published in Immunity, found that specialized immune cells called memory T cells - formed after first exposure to a pathogen - accumulate rapidly in the lungs and intestines through age 3 and more gradually in blood and lymph tissues. Immune cells in lungs and gut take time to mature Using a trove of tissue samples from deceased pediatric organ donors, Farber's team was able to pinpoint aspects of immune system development that distinguish babies from adults.
"But mice develop much more quickly than humans and their immune systems are a bit different than ours." "We know little about how the immune system develops throughout life, and most of what we know about immune system development in children comes from animal studies," says Donna Farber, PhD, an expert in immune system development at Columbia University Vagelos College of Physicians and Surgeons who led the research.
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