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GET TO KNOW YOUR IMMUNE SYSTEM WHEN BACTERIA AND VIRUSES ENTER YOUR BODY, THESE NATURAL DEFENDERS SPRING INTO ACTION    Macrophage This gargantuan white blood cell lies in wait within

healthy tissue. Sometimes years pass without action, but when a pathogen emerges, macrophages release a blast of proteins called cytokines, which calls the immune system into battle. From

there, the macrophage joins the cleanup crew by gobbling up dead and crippled pathogens. Natural Killer Cell Some infected cells can be rendered “invisible” to the immune system, which

allows the pathogen to continue to spread unabated. That’s when natural killer cells provide an extra layer of defense. A natural killer cell has the ability to identify abnormal cellular

appearance — as is often the case with cells infected by a virus. The killer cell studies its mark, and if the suspect cell appears to be infected, it releases proteins near the suspected

pathogen. The pathogen then eats the protein — a fatal, final meal. Neutrophil At the first sign of trouble, neutrophils swarm like killer bees with multiple stingers. Neutrophils can

capture their enemy, set traps, inject poison and amplify signals that pull in more immune-system warriors. Neutrophils only live for about a day, but as long as the battle continues, fresh

cells keep showing up to fight. Unfortunately, in their frenzy, they can often mistake healthy cells for the enemy. When that happens, and the neutrophils attack healthy tissue, the result

is inflammation, and inflammatory diseases, throughout the body. B Cell Although B cells don’t kill invaders directly, they help to slow down pathogens by covering them with sticky Y-shaped

proteins, robbing them of their strength and making them easy targets for cells like macrophages, which eat them in clumps. The B cell is an adaptive immune cell, meaning it is highly

effective against diseases it has battled before but struggles to recognize new pathogens. When a novel coronavirus arrives, it takes time to ramp up production of antibodies. T Cell The T

cell is one of the special-ops white blood cells called upon to “recognize” a foreign invader and know exactly how to fight it off. With new enemies like COVID-19, however, the process can

take weeks. Once the T cell learns the code — essentially mapping the molecular structure on a pathogen’s surface — it quickly trains an army of T cells to begin opening infected cells and

pumping them full of toxins. Doctors call this process immunity, although with COVID-19, we still aren’t certain how long it lasts.