biology

ICAM3

ICAM3 is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand ICAM3 rather than just read about it. In short: Intercellular adhesion molecule 3 (ICAM3) also known as CD50 (Cluster of Differentiation 50), is a protein that in humans is encoded by the ICAM3 gene. The protein is constitutively expressed on the surface of leukocytes, which are also called white blood cells and are part of the immune system.

Key takeaways

ICAM3 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect ICAM3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of ICAM3 from memory before moving on to harder problems.

Reference excerpt

Intercellular adhesion molecule 3 (ICAM3) also known as CD50 (Cluster of Differentiation 50), is a protein that in humans is encoded by the ICAM3 gene. The protein is constitutively expressed on the surface of leukocytes, which are also called white blood cells and are part of the immune system. ICAM3 mediates adhesion between cells by binding to specific integrin receptors. It plays an important role in the immune cell response through its facilitation of interactions between T cells and dendritic cells, which allows for T cell activation. ICAM3 also mediates the clearance of cells undergoing apoptosis by attracting and binding macrophages, a type of cell that breaks down infected or dying cells through a process known as phagocytosis, to apoptotic cells.

Protein structure ICAM3 is a 110–160 kDa protein that belongs to the intercellular adhesion molecule (ICAM) family. Like the other proteins in this family, ICAM3 is a type I transmembrane glycoprotein and consists in part of a hydrophobic transmembrane domain and a short domain that extends into the cytoplasm. ICAM3 also contains five extracellular immunoglobulin domains.

Function ICAM3 is found on the surface of leukocytes, and the ICAM3 gene is constitutively expressed in these cells. Interactions between ICAM3 and specific integrin receptors facilitate adhesion between cells.

Dendritic and T cell binding ICAM3 has an important function in the immune cell response, as it helps facilitate initial interactions between T cells and dendritic cells. Resting T cells show high levels of ICAM3 expression. ICAM3 on these T cells can bind to DC-SIGN, a transmembrane receptor present on dendritic cells, creating temporary contact between resting T cells and dendritic cells. This adhesion allows the T cell receptor (TCR) to interact with major histocompatibility complex (MHC) molecules on the surface of the dendritic cell, which, upon binding between the TCR, the MHC, and the peptide coupled to the MHC, facilitates T cell activation.

Apoptosis ICAM3 plays a role in apoptotic cell clearance by promoting the movement of macrophages, which ingest and break down unhealthy cells via phagocytosis, to cells undergoing apoptosis. Apoptotic cells can release extracellular vesicles containing ICAM3, which acts as a chemoattractant to phagocytes such as macrophages, directing them toward apoptotic cells. Apoptotic cells also contain altered ICAM3 proteins on their surface. These altered proteins allow macrophages to specifically target and bind apoptotic cells. This process is believed to involve binding between ICAM3 and CD14 receptors, which are a type of cell surface receptor expressed on macrophages and other phagocytes.

Mast cells ICAM3 is also found on mast cells, another type of leukocyte. Mast cells taken from human lungs and the HMC-1 line, a human mast cell line, both showed expression of ICAM3. ICAM3 helps mediate the adhesion of mast cells to the extracellular matrix.

Interactions

Dendritic and T cell binding Binding between ICAM3 and DC-SIGN, which takes place during initial interactions between T cells and dendritic cells, occurs with high affinity. This binding process is also calcium-dependent.

Apoptosis CD14, a receptor expressed on the surface of phagocytes, can also bind ICAM3. Interactions between CD14 and altered ICAM3 molecules on apoptotic cells are believed to help promote phagocytosis of apoptotic cells.

Integrins ICAM3 is a known ligand for LFA-1, an integrin expressed by leukocytes. To facilitate binding, the I domain of LFA-1 interacts with the ICAM3 protein's first immunoglobulin domain. ICAM3 also binds the integrin αDβ2.

Additional interactions ICAM3 has been shown to interact with activated ERM proteins, including ezrin (EZR) and moesin, in T cells.

Illustrations

Worked examples

Example 1 — a first encounter with ICAM3

Start with the simplest possible case. Write down what ICAM3 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to ICAM3 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about ICAM3 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of ICAM3

In research: ICAM3 appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses ICAM3 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: ICAM3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Clusters of differentiation, Genes on human chromosome 19, so understanding it makes those chapters shorter.
In everyday life: Look for ICAM3 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study ICAM3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what ICAM3 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain ICAM3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is ICAM3 in simple terms?

Why does ICAM3 matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study ICAM3?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on ICAM3.