Signaling proteins that alert the immune system an infection is present and that sometimes directly fight pathogens are the:

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Cytokines are signaling proteins that alert the immune system to the presence of an infection and can also directly fight pathogens. Complement proteins can also directly fight pathogens, but they are not specifically signaling proteins. Antibodies are produced by the immune system in response to an infection, but they do not signal the presence of the infection. Histamines and antihistamines are involved in allergic reactions and are not directly related to fighting infections.

Signaling Proteins That Alert the Immune System an Infection Is