Which of these cells is primarily involved in the body's first line of defense against pathogens?

The involvement of neutrophils in the body's first line of defense against pathogens is well-established due to their key role in the innate immune response. Neutrophils are a type of white blood cell that are part of the body's rapid response system to infection. When pathogens such as bacteria or fungi invade, neutrophils are among the first responders to arrive at the site of infection.

These cells are equipped with various mechanisms to recognize and eliminate pathogens quickly. They are capable of phagocytosis, which means they engulf and digest microorganisms. In addition to this, neutrophils can release reactive oxygen species and enzymes to destroy pathogens, making them essential for the initial defense against infections.

While B lymphocytes and plasma cells are critical components of the adaptive immune response, which develop later and involve a specific response to pathogens, they do not form part of the immediate first line of defense. Natural killer cells, on the other hand, provide a different form of defense by targeting virus-infected cells and tumor cells but are not typically the first responders to newly encountered pathogens.

In summary, the primary role of neutrophils in quickly responding to infections distinctly qualifies them as key players in the first line of defense within the immune system.