 Welcome back to our meds smarter lecture series where we're taking a smarter approach to preparing future physician Before we get started if you'll take just a quick minute and click that like button and also Subscribe and turn the bell on so that you'll be notified when we post new videos Let's talk about the major histocompatibility complexes We have major histocompatibility complex one and two these are all encoded by our HLA genes And what they do how they function is they give Antigen fragments to T cells and then they bind to the T cell receptors Okay, you can see kind in this little drawing over here this red spot in this drawing is going to be a peptide it is being Taken in by the major histocompatibility complex protein And it is attached to the cell membrane over here Which will then in turn present those fragments to T cells and the T cell receptors So let's talk about the different components from the histocompatibility complex one and two So I'm going to refer to both of these as MHC one and MHC two from now on and we're going to talk about Where it's located the binding site structures expressions functions antigen loading associated proteins in this particular chart So with MHC one the low side here are going to be HLA a b and c All right when we compare that to MHC two in just a minute You will see that there is one distinguishing factor and the thing you need to know is that MHC one loci I have one letter that's going to be one way that you can easily Remember this if there's one later HLA HLB HLC or HLA a HLA be HLAC then that is a MHC one component these bind to the TCR and CD8 receptors and They are made up of a long chain and a short chain What you'll see here is that it will express on all nucleated cells APCs and platelets with the exception of red blood cells So how does this work? This is going to take our endogenous antigens so viruses cytosolic proteins those kind of things and it's going to take it to the CD8 cytotoxic T cells Antigen peptides here are loaded onto the MHC one receptors at the rough endoplasmic reticulum and off after delivery via the transporter associated with the antigen processing proteins that are associated with MHC one are the beta two microglobulins So let's compare this to the MHC to MHC to like I said We are talking about something. That's not one letter because the MHC ones are one letter HLA a With MHC to we have two letters. So that makes it easy to MHC to two letters So we've got HLA DP HLA DQ and HLA DR The binding site for these are the TCR and the CD4 The structure of the MHC to Compound is two equal length chains. It is expressed on APCs And its function here is to present Exogenous antigens so bacterial proteins they're outside of the body to the CD4 helper T cells The antigen loading occurs Following the release of invariant chains in an acidified endozoom and associated proteins here are the invariant chain So let's talk finally here about the HLA subtypes that are associated with diseases so HLA A3 is going to be associated with Hemochromatosis you can remember that as HA3 Kind of begins that hemochromatosis word there B8 HLA B8 is associated with Addison's disease mystinia gravis and Graves disease So remember this as don't be late. So late sounds like eight Dr. Addison or else you'll send my patient to the grave. So remember my Patient to the grave so we were talking about B8 or be late Addison's disease mystinia gravis and Graves disease HLA B27 here is going to be associated with psoriatic arthritis Ankylosing spondylitis irritable bowel disease associated arthritis and Reactive arthritis so we can remember this by using the term pair PA IR So that's psoriatic arthritis Ankylosing spondylitis irritable bowel diseases and reactive arthritis. These are also seronegative Arthropathies Psoriasis here is associated with HLA C. Don't really have a good mnemonic here for you So you're just gonna have to remember HLA C is associated with psoriasis HLA DQ2 and DQ8. These are going to be associated with celiacs disease You can remember this as I8 so HLA 8 to HLA 2 Much gluten at Dairy Queen. All right So gluten is associated with celiacs disease. Dairy Queen is your DQ so DQ2 DQ8 HLA DR2 is associated with multiple sclerosis hay fever lupus and good pastor syndrome and You can remember this by using the mnemonic drive and DR specifically here. So DR2 is our HLA subtype drive to multiple hay pastures so multiple sclerosis Hey for hay fever and then pastures for good pastors. You'll also have to remember there SLE is also associated here HLA D3 is type 1 diabetes lupus or SLE graves disease Hashimoto's thyroiditis and Addison's disease. So remember 2, 3 SLE. All right. So in this case you can actually help out remembering that SLE is in DR2 and DR3 so DR2 DR3 SLE HLA DR4 is associated with rheumatoid arthritis another type 1 for diabetes and Addison's disease and Here the mnemonic is going to be there are four walls in One room. All right our OOM. We're using a different term or a different spelling here So that's going to be rheumatoid arthritis with DR4 And finally HLA DR5 is associated with Hashimoto's thyroiditis Remember this Hashimoto's is an odd doctor. All right. So odd. What are odd numbers? HLA D3 and HLA D5? for Hashimoto's thyroiditis so HLA D3 and 5 gives us Hashimoto's thyroiditis and Those are odd numbers associated with Hashimoto's disease If you found this material helpful for your studying Please like and consider subscribing to the channel also share this video so that more people can benefit from it like you have