HLA-DQ2

Key takeaways

HLA-DQ2 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HLA-DQ2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HLA-DQ2 from memory before moving on to harder problems.

Reference excerpt

HLA-DQ2 (DQ2) is a serotype group within HLA-DQ (DQ) serotyping system. The serotype is determined by the antibody recognition of β2 subset of DQ β-chains. The β-chain of DQ is encoded by HLA-DQB1 locus and DQ2 are encoded by the HLA-DQB1*02 allele group. This group currently contains two common alleles, DQB1*0201 and DQB1*0202. HLA-DQ2 and HLA-DQB1*02 are almost synonymous in meaning. DQ2 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ2 is most common in Western Europe, North Africa and East Africa. Highest frequencies are observed in parts of Spain and Ireland; this distribution correlates with the frequency of two of the most prevalent autoimmune diseases. There is also an increase in DQB1*0201 in Central Asia, peaking in Kazakhstan and declining slowly west to east into China and finally Southeast Asia. DQA1*0501 : DQB1*0201. DQ2.5 is one of the most predisposing factors for autoimmune disease. DQ2.5 is encoded, often, by a haplotype associated with a large number of diseases. This haplotype, HLA A1-B8-DR3-DQ2, is associated with diseases in which HLA-DQ2 has suspect involvement. Direct involvement of DQ2 is certain in coeliac disease (also known as celiac disease).

Serology

Serotyping efficiency. The serotyping efficiency of HLA-DQ2 is among the highest of the antisera. DQ2 antibodies can be used to effectively type DQ2 bearing individuals, however antibody may detect DQB1*0303.

Alleles

DQB1*0201 The DQB1*0201 allele is genetically linked to DQA1*0501 and DRB1*03. With DQA1*0501 it forms the DQ2.5cis encoding haplotype, with DRB1*03 it becomes part of the DR3-DQ2 (DR-DQ) serologically defined haplotype. With DQA1*0501 the allele is most frequently found in coeliac disease. With DR3 this DQ2 has the second strongest linkage to Type 1 diabetes, and when paired with HLA-DQ8 is the most abundant phenotype found in late onset, "Type1-Type2" diabetes mellitus type 1. As the incidence of coeliac disease is about 1% this allele is associated with more autoimmune disease relative to any other DQ haplotype. There are ambiguities regarding DQB1*0201 in the literature, some low resolution typing kits detect *0202 as *0201 and are presented as *0201 in the literature without distinction. DQB1*0201 in Europe is frequently found in the HLA A1-B8-DR3-DQ2 haplotype.

DQB1*0202 This allele is linked to several DQA1* alleles, the linkage with DQA1*0201 forms the DQ2.2 haplotype and linkage with DQA1*0303 forms the DQ2.3 haplotype. In Africa the DQA1*0501 haplotype is also linked rarely to DQB1*0202 and may represent that ancestral form of the DQ2.5 haplotype.

DQ2 isoforms and DQ2 haplotypes

DQ2.5 DQ2.5 refers to either a protein isoform and a genetic (chromosomal) haplotype. DQ2.5 isoform or heterodimer is shorthand for the cell surface receptor HLA-DQ α5β2. Frequently called 'the DQ2 heterodimer', the DQ2.5 isoform is actually one of two common DQ heterodimers, the other being DQ2.2. DQ2.5 haplotype is created by close genetic linkage of two alleles, written as a haplotype, DQA1*0501:DQB1*0201. The haplotype encodes DQ2.5cis isoform, referring to the cis arrangement of the DQA1*0501 and DQB1*0201 on the same variant of chromosome 6. The isoform can also be encoded trans-haplotype (between two sister chromosomes) forming the DQ2.5trans isoform. This isoform occurs when a person has the DQ7.5/DQ2.2 phenotype. DQ2.5 and the linked DR3 are associated with probably the greatest frequency of autoimmune occurrence relative to any other haplotypes. The haplotype is positively associated with coeliac disease, dermatitis herpetiformis, juvenile diabetes, Lambert–Eaton myasthenic syndrome (LEMS), Sjögren syndrome, and autoimmune hepatitis (although significant proportion of the risk is secondary to coeliac disease). DR3 and/or DQ2.5 are linked to the following diseases: Moreen's ulceration, "bout onset" multiple sclerosis, Graves' disease and systemic lupus erythematosus.

DQ2.2 DQ2.2 is shorthand for the DQ α2β2 heterodimeric isoform. The isoform is encoded almost exclusively by the DQA1*0201:DQB1*0202 haplotype. The haplotype is linked to DR7. A small percentage of coeliac disease are associated with this haplotype, and some disease causing gliadins are presented by DQ2.2. The haplotype is found at high frequencies in the Mediterranean and West Africa. The Eurasian geographic distribution of DQ2.2 is slightly greater than DQ2.5. Compared to DQ2.5, the frequency in Sardinia is low, but in Iberia it is high reaching a maximum frequency of ~30% in Northern Iberia, and half that in the British Isles. It extends along the Mediterranean and Africa at relatively high frequency and is found in high frequencies in some Central Asian, Mongolians, and Han Chinese. It does not appear to have an indigenous presence in the West Pacific Rim or the New World and DQ2.2 presence in Southeast Asia and Indonesia is likely the result of gene flow from India and China in post-Neolithic times. The haplotype shows considerable diversity in Africa and this has translated to Iberia with 2 addition haplotypes, DQA1*0303:DQB1*0202 and DR7:DQA1*0201:DQB1*0303. The expansion of DQ2.2 into Europe appears to have been slightly later or biased by some constriction between Iberia and the rest of the continent.

DQ2.3 DQ2.3 is shorthand for the DQ α3β2 heterodimeric isoform. The isoform is encoded by DQA1*0303:DQB1*0202 haplotype. The isoform can also be produced by phenotypes were one haplotype is DQ4.3, DQ7.3, DQ8.1, DQ9.3 and the other haplotype is DQ2.2 or DQ2.5. Therefore, the haplotype encoded receptor is a DQ2.3cis isoform which is genetically linked to DR7 By serology DR7-DQ2 cannot discriminate DQ2.2 from DQ2.3 haplotypes, and therefore DQA1 typing is required.

Other isoforms DQ2 beta chains can pair with trans to other alpha chain. However, there is no precedence in cis isoforms for DQ2, 4, 7, 8, or 9 binding DQ1 (DQA1*01) alpha chains. DQA1*03, *05 chains process to near identical alpha chains. The *04 chain can potentially complex with DQ2 forming DQ2.4. In East Asia there is the possibility of DQ2.6 resulting from pairing with DQA1*0601.

… excerpt ends here. Continue reading the full article.

Illustrations

HLA-DQ2: Isoform pairings in DQ2.5 homozygotes result in one isoform — Isoform pairings in DQ2.5 homozygotes result in one isoform

HLA-DQ2: Isoform pairings in DQ7.5/DQ2.2 result in 4 proteins isoforms, DQ2.5trans isoform is one(circled) — Isoform pairings in DQ7.5/DQ2.2 result in 4 proteins isoforms, DQ2.5trans isoform is one(circled)

Worked examples

Example 1 — a first encounter with HLA-DQ2

Start with the simplest possible case. Write down what HLA-DQ2 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 HLA-DQ2 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 HLA-DQ2 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 HLA-DQ2

In research: HLA-DQ2 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 HLA-DQ2 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: HLA-DQ2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Autoimmune diseases, Diabetes, HLA-DQ haplotypes, so understanding it makes those chapters shorter.
In everyday life: Look for HLA-DQ2 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.

How to study HLA-DQ2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HLA-DQ2 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 HLA-DQ2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HLA-DQ2 in simple terms?

HLA-DQ2 (DQ2) is a serotype group within HLA-DQ (DQ) serotyping system. The serotype is determined by the antibody recognition of β2 subset of DQ β-chains.

Why does HLA-DQ2 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 HLA-DQ2?

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 HLA-DQ2.