1/ A short #tweetorial introducing human leukocyte antigen (HLA) and typing...an important and often confusing topic in #transplantation #kidneytransplant

#FOAMed @MedTweetorials

What is an "HLA"?

HLAs = cell surface proteins encoded by highly polymorphic major histocompatibility complex (MHC) genes on Ch 6 🧬

In #transplantation, HLA proteins are #polymorphic antigens ➡️ alloreactive trigger for the immune response ➡️ can ultimately lead to organ #rejection ☠️
3/ The 2 primary classes of MHC molecules are 1⃣ and 2⃣.

Class 1⃣ MHC are found on the cell surface of ALL nucleated cells + platelets. Their role is to present intracelleular peptide fragments to CD8 #Tcells
Class 2⃣ MHC are found on the surface of "pro" antigen presenting cells (APCs), e.g. dendritic cells, B cells, mononuclear phagocytes, some endothelial cells.

They present extracellular peptides that are phagocytosed, digested in lysosomes ➡️ loaded onto class 2⃣ molecule
5/ 3 major genes encoded by class 1⃣ & 2⃣ HLA = A/B/C & DR/DP/DQ, respectively

Back to "polymorphic" - what does it mean?

A gene = polymorphic if > 1⃣ allele occupies that gene's locus within a population. So, there are hundreds of alleles that can occupy HLA loci above. 👇🏽
6/ We have 2⃣ alleles at each HLA locus: 1⃣ from biological mother & 1⃣ from biological father. This is co-dominant inheritance, both alleles are fully expressed.

Loci are inherited in a haplotype = combo of alleles at adjacent loci on a chromosome that are inherited together.
7/ HLA typing using 🧬 PCR techniques can be performed to identify one's HLA alleles. Allele level typing is > specific than serologic typing. 2 may share a SEROLOGIC type of 2 at the HLA-A locus - but both may have different A2 alleles.

Remember - HLA genes are POLYmorphic!
8/In summary,

1⃣ #HLA genes = highly polymorphic & encode cell surface proteins
2⃣Class I/II HLA present intra/extracellular peptides ➡️ CD8/CD4 #Tcells, respectively
3⃣The major Class I/II genes = A/B/C & DR/DP/DQ, respectively
4⃣Co-dominant inheritance

Next: Crossmatching!
Missing some Tweet in this thread? You can try to force a refresh.

Enjoying this thread?

Keep Current with Samira Farouk, MD, MS, FASN

Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

Twitter may remove this content at anytime, convert it as a PDF, save and print for later use!

Try unrolling a thread yourself!

how to unroll video

1) Follow Thread Reader App on Twitter so you can easily mention us!

2) Go to a Twitter thread (series of Tweets by the same owner) and mention us with a keyword "unroll" @threadreaderapp unroll

You can practice here first or read more on our help page!

Follow Us on Twitter!

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just three indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3.00/month or $30.00/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!