# Adalimumab p55 p75 TNF receptor binding

## Adalimumab does not directly bind to p55 or p75 TNF receptors; instead, it binds to TNFα and sterically blocks TNFα from engaging these receptors.

## Abstract

No studies directly measured adalimumab binding to isolated p55 (TNF-RI) or p75 (TNF-RII) receptors. Instead, adalimumab exerts its effects by binding to TNFα with high affinity (30.4 pM) and sterically blocking TNFα-receptor interactions through epitope overlap with the TNFR2 binding site. The adalimumab epitope comprises discontinuous TNFα segments with a buried surface area of 2,540 Ų, competitively inhibiting TNFα binding to both receptor subtypes and preventing activation of downstream signaling pathways including NF-κB. Functional studies revealed differential effects on receptor preservation: adalimumab at 16.7 nM maintained TNF-RI surface expression at baseline levels while TNF reduced it 2.4-fold, whereas all anti-TNF biologics equally prevented TNF-RII loss. Blocking antibody studies confirmed that TNF-RI is the predominant receptor mediating TNF-dependent cellular responses, which adalimumab inhibits by restricting TNF access to this receptor.

These findings indicate that adalimumab does not directly bind p55 or p75 receptors, but rather blocks TNFα from engaging these receptors, with functional selectivity favoring TNF-RI preservation through mechanisms independent of the Fc domain.

## Methods

We analyzed 10 sources from an initial pool of 200, using 7 screening criteria. Each paper was reviewed for 6 key aspects that mattered most to the research question.

Records from Elicit search:

- n = 200 Papers screened using: Adalimumab Binding Mechanisms, Specific TNF Receptor Types, Binding Measurements, Appropriate Study Design, Mechanistic Data Inclusion, Adalimumab Focus, Study Type Quality
- n = 200 Papers screened out
- n = 190 Papers included for extraction

## Paper search

We performed a semantic search across over 138 million academic papers from the Elicit search engine.

We ran this query: “Adalimumab p55 p75 TNF receptor binding.”

The search returned 200 total results from Elicit.

## Screening

We screened in sources based on their abstracts that met these criteria:

- **Adalimumab Binding Mechanisms**: Does this study investigate adalimumab’s binding mechanisms or interactions with TNF receptors?
- **Specific TNF Receptor Types**: Does this study examine TNF-α receptor p55 (TNFR1) and/or p75 (TNFR2) in relation to adalimumab?
- **Binding Measurements**: Does this study measure binding affinity, receptor occupancy, or molecular interactions?
- **Appropriate Study Design**: Is this study an in vitro, in vivo, ex vivo experimental study, clinical trial, or pharmacokinetic/pharmacodynamic study?
- **Mechanistic Data Inclusion**: Does this study include mechanistic data on TNF receptor binding (not solely clinical outcomes)?
- **Adalimumab Focus**: Does this study focus on adalimumab specifically, or if it studies other TNF inhibitors, does it include direct comparison to adalimumab?
- **Study Type Quality**: Is this study a full research article (not a case report, editorial, opinion piece, or conference abstract without full-text publication)?

We considered all screening questions together and made a holistic judgement about whether to screen in each paper.

## Data extraction

### TNF Receptor Binding Data:
- Binding affinity values (KD): 7.05 × 10^-11 M to 1.0 × 10^-10 M.
- No specific data for p55 (TNF-RI) and p75 (TNF-RII) separately. 
- No association and dissociation rates (kon, koff).
- No avidity measurements.
- No binding stoichiometry.
- No surface plasmon resonance data.
- No competition binding results.
- No quantitative binding parameters specific to p55 and p75.

### Receptor Expression Effects:
- Not mentioned (the paper does not provide specific data on receptor expression effects such as changes in surface receptor levels, receptor internalization, or flow cytometry data).

### Binding Mechanism:
- Epitope mapping data: The Adalimumab epitope on TNFα includes residues TNF Pro-19, TNF Gln-20, TNF Glu-23, TNF Lys-65 to TNF Gln-67, TNF Glu-10 to TNF Pro-113, TNF Tyr-141, and TNF Ala-145 to TNF Glu-146 and TNF Thr-71, TNF His-72, TNF Thr-77, TNF Thr-79, TNF Ser-81, TNF Lys-89 to TNF Asn-91, and TNF Glu-135 to TNF Asn-137 of an adjacent TNFα protomer.
- Crystal structure information: The crystal structure of the TNFα-adalimumab Fab complex shows a large and highly complementary interface with a total buried surface area of 2,540 Ų.  
- Competitive inhibition with natural TNF-receptor binding: Adalimumab competitively inhibits the binding of TNFR to TNFα by occupying the receptor-binding site.
- Whether binding blocks TNF access to receptors: Yes, Adalimumab blocks access to receptors by steric blocking and preventing ligand binding.

### Functional Consequences:
- Adalimumab binding to TNFα prevented the activation of TNFRs, which are involved in signaling pathways such as NF-κB. 
- Adalimumab completely inhibited TNF-induced apoptosis in a dose-dependent manner.

### Experimental Methods:
- Binding assay techniques: Surface Plasmon Resonance (SPR) using BIAcore T100.
- Assay conditions: Contact time - 300 seconds; Flow rate - 30 l/min.

### Comparative Analysis:
- Binding affinity measurements revealed differences among TNF inhibitors. Adalimumab demonstrated a binding affinity of 30.4 pM, compared to infliximab at 27.3 pM and etanercept at 11.8 pM. 
- The clinical advantages of adalimumab over infliximab and etanercept were attributed to its direct inhibition mechanism through substantial overlap with the TNFα-TNFR2 interface, resulting in higher efficacy in autoimmune diseases.

## Synthesis

The reviewed studies reveal a consistent mechanism whereby adalimumab blocks TNF receptor signaling primarily through competitive inhibition rather than direct receptor binding. No studies provided direct binding affinity measurements for adalimumab to isolated p55 or p75 TNF receptors. Instead, the evidence indicates that adalimumab exerts its effects by binding to TNFα and sterically blocking its interaction with cell surface receptors.

The differential preservation of TNF-RI versus TNF-RII by adalimumab compared to other agents can be mechanistically explained by the size and nature of immune complexes formed. Adalimumab forms larger complexes (3 antibodies:1-2 TNF trimers) compared to etanercept’s 1:1 complexes.

The superior functional outcomes of adalimumab compared to infliximab in monocyte assays appear paradoxical given that infliximab has slightly higher binding affinity. However, this is explained by epitope positioning: adalimumab’s epitope overlaps more substantially with the TNFα-TNFR2 binding interface, achieving more complete steric blockade despite marginally lower affinity.