The p24 antigen is a constituent protein of the capsid of the HIV virus. It is secreted into the blood during infection. The level of p24 antigens in the blood is used as a direct marker of virus multiplication.

Neurofilament light chain (NfL) is an intermediate filament protein that constitutes intermediate filaments, a part of the cytoskeleton, of neurons (intermediate filaments are sometimes referred to as nanofilaments). Together with the other four neuronal intermediate filament proteins, namely neurofilament heavy chain, neurofilament medium chain, alpha-internexin and peripherin, NfL assembles into neurofilaments, which are important for dendritic branching and growth and stability of axons in both central and peripheral nerves and for post-traumatic axonal regeneration. Axonal damage leads to NfL release into the extracellular space.