system
Given the following post, respond as if you're commenting on Reddit:
human
I have a cold and am curious, what defenses will the virus encounter (in order, from entry)?
gpt
First, there are physical barriers.  Skin, for example.  Then, assuming you got it through contact between your mucous membranes (mouth, nose, eyes) and particles containing the virus, there are antimicrobial agents in these mucous membranes (though most of these are geared toward being antibacterial, not antiviral) as well as the actual fluid (tears, saliva, mucous) presenting something of a barrier as well.  

Most colds are infections of the upper part of the throat.  Viruses enter cells and begin to replicate inside them.  Interestingly, most rhinoviruses use a receptor called ICAM1 to enter the cell, and up its production once they're inside.  However, ICAM1 is also a signalling molecule, and it signals to macrophages (cells of the immune system) and starts a signalling cascade which leads to cytokine release, signalling, and imflammation, which gives you the local effects (sore throat) and broader effects like runny nose and fever.  Furthermore, cells like leukocytes can phagocytose (essentially, eat) virus or destroy infected cells.  These steps are generally referred to as cell-mediated immunity.

Meanwhile, B-lymphocytes are running around.  If a lymphocyte whose antibody matches the virus is found, that cell is activated (this requires interacting with a T "helper" cell).  The B cell differentiates into "memory" B cells, that stay around to remember the antibody in case of reinfection later, and plasma cells, that divide rapidly and start churning out the antibody.  This part is generally called humoral or antibody immunity.  The antibodies bind to the virus, which prevents virus particles from getting into cells and identifies them to other players in the immune system which can come along and scoop them up.  At this point, the infection is generally cleared rapidly, unless the person is immunocompromised.