LL-37 (Human Cathelicidin) vs Thymosin Alpha 1

LL-37 (Human Cathelicidin)

LL-37 is a 37-residue peptide cleaved from hCAP18, the only human cathelicidin; its name refers to its two leading leucines and its length. It is made by neutrophils and by epithelial cells of the skin, gut and airways, and the gene that encodes it is regulated in part by vitamin D. Laboratory studies have examined its activity against bacteria, fungi and some viruses, and its signalling to host immune and epithelial cells. Its research record runs in two directions: it is studied as a host-defence molecule and also as a contributor to inflammatory skin conditions such as psoriasis and rosacea. Most published work is in vitro or in animals, and interventional human studies are few and small.

Thymosin Alpha 1

Thymosin alpha 1 is a 28-residue peptide, acetylated at its N-terminus, first isolated from calf thymus extract and now made synthetically. It matches the N-terminal segment of a larger protein, prothymosin alpha, from which it is thought to be released by proteolytic processing; the synthetic form is also known as thymalfasin. The peptide is strongly acidic and, in water, largely unstructured. Its literature spans cell studies of immune signalling, animal infection and tumour models, and human clinical studies in chronic viral hepatitis, severe infection and vaccine response. Many of those clinical studies are small, and a defined cellular receptor has not been confirmed.

How LL-37 (Human Cathelicidin) acts

In dilute aqueous solution LL-37 is largely disordered; on contact with lipid membranes it has been reported to fold into an amphipathic α-helix. Its side chains give it a net charge of about +6 at neutral pH, which draws it to the negatively charged surfaces of bacterial membranes, and it is thought to permeabilise those membranes. It also binds bacterial lipopolysaccharide. On host cells it has been reported to act through several receptors, among them formyl peptide receptor 2 and the P2X7 purinergic receptor, and to transactivate the epidermal growth factor receptor in keratinocytes. Complexes of LL-37 with self-DNA or RNA have been reported to activate Toll-like receptor signalling in dendritic cells, a pathway examined in psoriasis research.

How Thymosin Alpha 1 acts

Thymosin alpha 1 has no single confirmed receptor. Several studies have linked its activity to Toll-like receptor signalling, particularly TLR9 and TLR2 in dendritic cells, with downstream activation of pathways including NF-κB and p38 MAPK. In cell and animal models it has been reported to influence T-cell maturation, production of cytokines such as interleukin-2 and interferon-gamma, and natural killer cell activity. Structural studies report that it becomes partly helical in membrane-like environments, which has been proposed as relevant to how it interacts with cells, though this remains an open question.

The records side by side

• Type: LL-37 (Human Cathelicidin), Antimicrobial peptide (cathelicidin); Thymosin Alpha 1, Acetylated thymic peptide
• Length: LL-37 (Human Cathelicidin), 37 amino acids; Thymosin Alpha 1, 28 amino acids
• Molecular weight: LL-37 (Human Cathelicidin), 4493 g/mol; Thymosin Alpha 1, 3108.3 g/mol
• Molecular formula: LL-37 (Human Cathelicidin), C205H340N60O53; Thymosin Alpha 1, C129H215N33O55

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.