Neutrophils are part of the body's host-defense system, migrating from the bloodstream into tissues in response to bacterial infection. However, this normal function is counterproductive when an organ is transplanted from another person. More selective inhibitors of the immune system are desirable. Both proteins and peptides are complex molecules made up of chains of amino acids. Proteins are more complex, and of higher molecular weight, often consisting of several hundred amino acids.
Peptides are smaller, low molecular weight compounds, sometimes as small as two amino acids.
For comparison, a monoclonal antibody molecule can consist of several thousand amino acids. The interactions of drugs with the metabolism of the living body over time. These may include absorption, distribution, biotransformation, localization in tissues, breakdown, destruction and excretion. Data from PK studies are used to assess dosage, method of administration and to understand how the drug interacts with the body. Most large clinical trials also gather some PK data.