Enzyme-catalyzed reactions are prone to inhibition by molecules that interfere with the formation of product. Many drugs for the treatment of disease function by inhibiting enzymes. For example, an important strategy in the treatment of acquired immune deficiency syndrome (AIDS) involves the steady administration of a specially designed protease inhibitor. The drug inhibits an enzyme that is key to the formation of the protein envelope surrounding the genetic material of the human immunodeficiency virus (HIV). Without a properly formed envelope, HIV cannot replicate in the host organism.

- in AIDS, microglia become phagocytic.
- If helper T cell activities are non-functional, a state of immunodeficiency results.  This means that potentially pathogenic organisms, which are normally kept in check by the immune system, may proliferate and cause overt pathology, e.g., acquired immune deficiency syndrome (AIDS), where a virus (HIV I) specifically infects and kills (predominantly) helper T cells, but also a variety of antigen-presenting cells.
- Bell's Palsy can be a complication in patients with AIDS.
- Fusion to form multinucleated giant cells in CNS is a response to microglia infected with HIV.