One of the substances they include is histamine, when they release histamine it causes the blood vessels to dilate and make them leaker. This makes it easier for many types of white blood cells, such as macrophages to come. And these terrifying things consume us pathogens.
White blood cells
Another way the second line of defense tries to fight us is by increasing the temperature in the human body which triggers the mast cells who produce histamine which increases the permeability of the capillaries to white blood cells. Then T cells are called to come to the infection site which causes inflammation.
Second line of defense
After that if some of us still manage to get past that we move on to the third line of defense in the immune system. This process takes place when one of us has a cold virus spreading in their body they start targeting us. This is when the adaptive immunity takes place which is basically a response to antigens and only that. The antigens are a part of us (pathogens).