HLA DR3-DQ2

Key takeaways

HLA DR3-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 DR3-DQ2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HLA DR3-DQ2 from memory before moving on to harder problems.

Reference excerpt

HLA DR3-DQ2 is a double serotype that specifically recognizes cells from individuals who carry a multigene HLA DR, DQ haplotype. Certain HLA DR and DQ genes have known involvement in autoimmune diseases. DR3-DQ2, a multigene haplotype, stands out in prominence because it is a factor in several prominent diseases, namely coeliac disease and juvenile diabetes. In coeliac disease, the DR3-DQ2 haplotype is associated with highest risk for disease in first degree relatives, highest risk is conferred by DQA1*0501:DQB1*0201 homozygotes and semihomozygotes of DQ2, and represents the overwhelming majority of risk. HLA DR3-DQ2 encodes DQ2.5cis isoform of HLA-DQ, this isoform is described frequently as 'the DQ2 isoform', but in actuality there are two major DQ2 isoform. The DQ2.5 isoform, however, is many times more frequently associated with autoimmune disease, and as a result to contribution of DQ2.2 is often ignored. The frequency of both diseases changes concerning both the environment (diet) and the frequency of the DR3-DQ2. With coeliac disease risk is increased with the consumption of Triticeae glutens, and this also increases risk in juvenile diabetes whereas other cereals also appear to play a role. More importantly the risk of disease is greatest in homozygotes and linear increases in haplotype result in several fold increases in disease risk. This increased risk is most prominent in a rare cancer, enteropathy associated T-cell lymphoma. HLA-DR3-DQ2 is found in HLA A1-B8-DR3-DQ2 haplotype in Northern Europeans (including the British Ilse, Ireland, Iceland).

Genetic Linkage HLA DR3-DQ2 is the serotypic representation of a HLA-DRB1:DQA1:DQB1 cis-chromosomal haplotype on human 6p21.3 in a region known as the HLA complex. The DR3-DQ2 haplotype is notable because of the very strong linkage between genes that extends into the HLA-A, -B and -C regions of the HLA gene complex in northern and northwestern Europe. The linked haplotype is HLA A1-B8-DR3-DQ2 (AH8.1 in the most recent literature) Because of its strong linkage disequilibrium, each of the genes in the haplotype are markers for probable presence of adjacent genes. However serotyping does not recognize genes, but clusters of gene products. For example, DQ2 recognizes both DQB1*0201, DQB1*0202, DQB1*0203. DQB1*0202 is not genetically linked to DQA1*0501 and its cis-haplotype isoform infrequently mediates coeliac disease or type 1 diabetes. For serotypic identification of the DQ2.5cis isoform requires the DR3 (or HLA-DR17 or HLA-DR18) and DQ2 serotypes. An example of phenotypes that can mediate CD and T1D, the DR3-DQ2/X serotypes and the DR5-DQ7/DR7-DQ2 serotypes can mediate celiac disease with equal efficiency but the DR5-DQ7/DR7-DQ2 cannot mediate T1D as successfully as DR4-DQ8 or DR3-DQ2 (X is not DR3-DQ2 or DR7-DQ2).

Distribution HLA DR3-DQ2 is not spread evenly among humans. It has a substantially higher frequency in the western world, except indigenous Native American (see tables). It is virtually absent in some Asian populations. It current world distribution suggest that it spread from Africa with a wave that spread late in human evolution which reached central Asia more recently, a possibility is that it spread with agrarian cultures that migrated from Africa. [Note some population test DR3 or DQA1:DQB1, the DR3-DQ2 serotype is generally synonymous in frequency with DQ2.5]

Frequencies in Africa

DR3-DQ2 probably originated from Central or West Africa. DQ2.5cis haplotype is the second highest frequency haplotype in the Aka (N. Congo) and several other surrounding groups it is virtually absent in the !Kung. DQ2.5 primarily spread to the northwest and appears to have spread late in global spread of anatomically modern humans. The !Kung and Austronesians are reasonable marker populations earliest (eatward) spread out of Africa and those that spread rapidly, since the ancestors of the !Kung appear to have come from East Africa and share many Cw_B types in common with Austronesians and Northern Eurasians. DQ2.5 is at low frequencies in both of these populations, and it did not spread to Japan or the New World in pre-Columbian times. There is the possibility it spread to Arabia, but through stepwise expansion of small groups was lost from the DQ genetic repertoire. DQ2.5 appears to be derived from DQ2.2 by gene recombination. One haplotype DQA1*0501:DQB1*0202 can be found in Africa suggesting DQB1*0201 evolved from DQB1*0202. The regions of Africa where DQ2.5 is at its highest frequencies indicate potential sources for western European haplotypes (e.g. bedoin) but also indicate recent dispersion making precise evolution difficult to interpret. Other evidence for a west African origin/expansion is seen with the probable origin of DQA1*0501 from DQA1*0505, which is at relatively high frequencies in west-central Africa.

Frequencies in Europe

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with HLA DR3-DQ2

Start with the simplest possible case. Write down what HLA DR3-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 DR3-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 DR3-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 DR3-DQ2

In research: HLA DR3-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 DR3-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 DR3-DQ2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics HLA-DQ haplotypes, HLA-DR haplotypes, Human MHC haplogroups, so understanding it makes those chapters shorter.
In everyday life: Look for HLA DR3-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 DR3-DQ2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HLA DR3-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 DR3-DQ2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HLA DR3-DQ2 in simple terms?

HLA DR3-DQ2 is a double serotype that specifically recognizes cells from individuals who carry a multigene HLA DR, DQ haplotype. Certain HLA DR and DQ genes have known involvement in autoimmune diseases.

Why does HLA DR3-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 DR3-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 DR3-DQ2.