your skin covers almost all parts of your body to prevent infection from pathogens, your nose has hairs within them which act as a physical barrier to infection, mucus is produced by goblet cells in your nose, throat and trachea, mucus traps dust and pathogens, pathogens in mucus are wafted by ciliated cells to your throat and swallowed, stomach acid kills pathogens. These things are general rather than targeted at one particular illness. They are first line defences. If pathogens get past the non-specific defence systems, there are other systems in place such as antibodies as a second line of defence.