What is a second line of defense against virus and antigen invasion in organisms?

The second line of defense against viral and antigen invasion in organisms primarily involves the immune responses that take place after the initial physical barriers, like skin and mucous membranes, have been breached. Interferons and phagocytosis are key components of this second line of defense.

Interferons are signaling proteins produced by cells in response to the presence of viruses and help to establish an antiviral state in neighboring cells. They play a crucial role in the immune response by interfering with viral replication and activating immune cells.

Phagocytosis, on the other hand, is the process by which certain immune cells, such as macrophages and neutrophils, engulf and digest pathogens, including viruses and antigens. This action not only helps to eliminate the invaders physically but also presents antigens from the pathogens to other immune cells, facilitating a more tailored adaptive immune response.

Together, these processes enhance the body's ability to respond to infections beyond the barriers of skin and mucous membranes, representing a vital part of the innate immune response that acts immediately or within hours of a pathogen's appearance in the body.