Complement System | Classical Pathway

The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. It is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime. The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system.
The complement system consists of a number of small proteins that are synthesized by the liver, and circulate in the blood as inactive precursors. When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages.
Most of the proteins and glycoproteins that constitute the complement system are synthesized by hepatocytes. But significant amounts are also produced by tissue macrophages, blood monocytes, and epithelial cells of the genitourinary system and gastrointestinal tract. The three pathways of activation all generate homologous variants of the protease C3-convertase. The classical complement pathway typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells. The mannose-binding lectin pathway can be activated by C3 hydrolysis or antigens without the presence of antibodies (non-specific immune response). In all three pathways, C3-convertase cleaves and activates component C3, creating C3a and C3b, and causes a cascade of further cleavage and activation events. C3b binds to the surface of pathogens, leading to greater internalization by phagocytic cells by opsonization.
The classical pathway is triggered by activation of the C1-complex. The C1-complex is composed of 1 molecule of C1q, 2 molecules of C1r and 2 molecules of C1s, or C1qr2s2. This occurs when C1q binds to IgM or IgG complexed with antigens. A single pentameric IgM can initiate the pathway, while several, ideally six, IgGs are needed. This also occurs when C1q binds directly to the surface of the pathogen. Such binding leads to conformational changes in the C1q molecule, which leads to the activation of two C1r molecules. C1r is a serine protease. They then cleave C1s (another serine protease). The C1r2s2 component now splits C4 and then C2, producing C4a, C4b, C2a, and C2b (historically, the larger fragment of C2 was called C2a but is now referred to as C2b). C4b and C2b bind to form the classical pathway C3-convertase (C4b2b complex), which promotes cleavage of C3 into C3a and C3b. C3b later joins with C4b2b to make C5 convertase (C4b2b3b complex).

[@sunaibarazaq06]

Sir you mentioned that C2 is an exception as it's "a" fragment(C2a) is larger, active and it along with C4b later forms C3 convertase(C4b2a) but sir with due respect in LANGE MICROBIOLOGY 16TH EDITION, it's mentioned that C3 convertase is formed by C4b2b, which leaves me confused. Kindly clear the confusion.

[@hussainbiology]

Yes....C3 is now c4b2b.....
i have made this video 2 years ago and this is latest research.

[@sunaibarazaq06]

@@hussainbiology thank you so much sir

[@hussainbiology]

@@sunaibarazaq06 Most welcome....✌️

[@safesoundequine8511]

They changed the way they refer to it recently, it was previously always called 2a but since it was confusing now it's called 2b.

[@dominicdovalis5620]

These videos and your teaching style are fantastic. Much easier to understand than simply reading out of a textbook. Will definitely be coming back to your page for other topics. Thank you for what you do!

[@hussainbiology]

Glad you like them! thanks for appreciation

[@0Jake0Eden0]

Beautiful video. Clear, concise and well illustrated. I think you've saved a lot of people a lot of time. Thanks heaps

[@hussainbiology]

thanks for appreciation..Glad to know that it helps

[@favourkessington1630]

It really cool how these videos and the complement system are short and straight to the point

[@hussainbiology]

thanks for appreciation

[@aaliyahtrujillo5621]

This is such a well explained and thorough video. The outro at 5:22 topped it out, 10/10 recommend for all pre med and Nursing students, I would also watch again simply for the outro

[@hussainbiology]

thanks Aaliyah for appreciation...glad it helps

[@samamahmood8008]

Thank you for a greatly simplified and well prepared video!
Small note: C3 convertase is now C4b2b

[@hussainbiology]

thanks for appreciation and ur feedback ✌️✌️

[@hussainbiology]

Really C3 Convertase is now C4b2b???
if it is so then C5 Convertase also becomes C4b2b3b right ??

[@samamahmood8008]

Yes it is

[@RainMist89]

@@hussainbiology you had this right the first time C4b2a

[@alstroemeria2466]

may I know where you got this from, any reference book or journal?

[@RookieGamerz-3110]

I was taught this months ago by our teacher and i already forgot everything. Thank you very much. This was such an precise video.

[@hussainbiology]

Glad it was helpful!

[@himynameisjakeable]

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[@alphabaiters3783]

Was sent to read this from the textbook and did not understand. Thank you so much for this video it helped a lot!!

[@hussainbiology]

thanks for appreciation.. Glad to know that it helps ✌️

[@HealthyVlogsByDnyan]

Wow, such and amazing explanation of this complex pathway, thank you so much!

[@hussainbiology]

thanks for appreciation ☺️

[@laboratoryspace3135]

Crystal Clear Concept!!!! Hats off to your stunning hardwork for this lect!❣️

[@hussainbiology]

thanks for appreciation.
Glad u like it

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[@drtimndika]

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[@hussainbiology]

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I was honestly scared to learn this but you made it so easy ! Thank you so much

[@hussainbiology]

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[@hussainbiology]

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Amazing explanation!

[@zbs8334]

I love you for this! Finally understand compliment after hours of studying.

[@hussainbiology]

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[@tehreemfarooq8329]

Oh wow!! Now classical pathway seems to make sense✌

[@hussainbiology]

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[@raminbarzani8977]

It makes much more sense with the animation. Thanks!

[@hussainbiology]

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Needed this a day before exams and makes me confident

[@hussainbiology]

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[@manoharkyasarapu8356]

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[@hussainbiology]

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Thank you sir 🙏

[@hussainbiology]

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[@Sophie23456]

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[@hussainbiology]

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Glad to know that it helps ✌️

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Great video, thanks.

[@hussainbiology]

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[@haridineevikhe8549]

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[@hussainbiology]

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[@satyasripothavarjula9276]

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[@hussainbiology]

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WOW! Very easy and simple explanation!

[@hussainbiology]

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YOU ARE AMAZING

[@347pallavipandey9]

Time consuming explanation. Not everyone has that quality.Thank you so so much sir.

[@hussainbiology]

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[@shreyapoudyal4114]

Good explanation in simple and easy way... this helped me ..thank you from 🇳🇵

[@hussainbiology]

thanks for appreciation 😊

[@weiderjobanidiaz638]

A really good explanation :) Greetings from Colombia!
PD: Could you recommend me a book about immunology, please? Im really interested in this field.

[@hussainbiology]

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[@SMR_travels]

Immunology by Elgert is very useful in understanding this...

[@05.abiramiindhu77]

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[@almasmalik1812]

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[@hussainbiology]

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[@hussainbiology]

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[@hussainbiology]

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[@hussainbiology]

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[@hussainbiology]

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[@mercywakwaini5718]

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[@hussainbiology]

thanks for appreciation.... Glad it helps

[@creatart6790]

Nice video sir..

[@hussainbiology]

thanks Sammi for appreciation....Glad to know that it helps

[@florencenight9033]

Sir may I ask why is not C4bC2B but instead is C4BC2A? Because I saw some of the books stating C4BC2A

[@ayushpunwatkar8641]

Thank u sir💯

[@hussainbiology]

You are welcome

[@Docanipa]

once u said a fragment is smaller and inactive then said when c bind with a it become active why is that

[@DevPatel-fs8ku]

Damn! That's awesome

[@hussainbiology]

thanks

[@sthevanusmoe6496]

thank you sir you saved me

[@hussainbiology]

thanks for appreciation

[@nicewoman2900]

In this video you said that calssical pathway are antiboby dependent, and in the lectin video you said that classical pathway is antibody independent. whith is correct now?

[@sanamir6343]

Great job

[@hussainbiology]

thanks Sana for appreciation....✌️

[@muhju9610]

Great

[@malithidilrangi4368]

How many antibodies are needed minimum and maximum to activate the complement system?

[@dhanyapy3041]

Superb..thanks

[@hussainbiology]

😊

[@dhanyapy3041]

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[@mahanasir8834]

well explained

[@hussainbiology]

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[@ajmerjaiswal3941]

Awesome

[@hussainbiology]

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[@saimarashid3518]

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[@hussainbiology]

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[@biology_mcqs3037]

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[@biology_mcqs3037]

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[@hussainbiology]

Most wlcm

[@manashpratimsarmah4487]

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[@sunaibarazaq06]

Thank you so much. It was really helpful.
Are you a Kashmiri though? Sound very much like a Kashmiri😄❣

[@hussainbiology]

Most Welcome Sunaiba...
and yes i am Kashmiri....
Are u too ???

[@sunaibarazaq06]

@@hussainbiology yes sir.

[@mansipatel704]

Very easy

[@zirwazubair7563]

Classical pathway innate r adaptive??

[@hussainbiology]

Plays role in both innate as well as in Adaptive immunity but it is more pronounced during innate immune system.

[@tanu6464]

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[@user-nf7un9fn5h]

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[@hussainbiology]

No dear .....

[@admazainab6324]

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[@hussainbiology]

Yes Zainab i am from Kashmir ✌️

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[@rizwanulislam444]

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[@hussainbiology]

Varmul

[@rizwanulislam444]

Kashmir

[@hussainbiology]

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[@sharanyamistry8289]

Sir where r u form

[@hussainbiology]

Kashmir...

[@CabdifataaxCardiologist]

May Allah guides you to the light of Islam ☪️ and if u are believer may Allah make u steadfast to faith of Islam ☪️

[@hussainbiology]

Ameen

[@drtimndika]

Right

[@extrawork3263]

Everything is clear but what is compliment system 🥲 trying to figure this out our today's lesson