WHY this note exists: B cells aur T cells dono lymphocytes hain (ek type ke white blood cells) aur dono bone marrow se aate hain. Phir bhi ye infection se bilkul alag-alag tareekon se ladte hain. Agar tum inhe alag nahi kar sakte, toh poora adaptive immune system ek dhundh ban jaata hai. Ye note tumhe ek first-principles tarika deta hai taaki tum inhe kabhi confuse na karo.
Har nucleated cell apne khud ke internal proteins ke bits MHC class I par display karta hai. Agar andar koi virus hai, toh viral peptides yahan dikhai dete hain. → Cytotoxic (CD8) T cells MHC-I read karte hain aur us cell ko kill kar dete hain.
Specialised antigen-presenting cells (macrophages, dendritic, B cells) bahari cheezein niggal lete hain aur unhe MHC class II par display karte hain. → Helper (CD4) T cells MHC-II read karte hain aur cytokines release karte hain taaki B cells aur cytotoxic cells boost hon.
Kaun sa cell type humoral (antibody) immunity drive karta hai?
B cells
Kaun sa cell type cell-mediated immunity drive karta hai?
T cells
Ek activated B cell kya ban jaata hai, aur kya secrete karta hai?
Ek plasma cell; antibodies secrete karta hai
Kya T cells free/whole antigen recognise kar sakte hain?
Nahi — sirf antigen tab jab MHC molecules par presented ho
Kaun sa T cell infected cells KILL karta hai aur kaun sa MHC class read karta hai?
Cytotoxic CD8 T cell, MHC class I read karta hai
Kaun sa T cell doosri cells HELP karta hai aur kaun sa MHC class read karta hai?
Helper CD4 T cell, MHC class II read karta hai
CD–MHC pairing ke liye memory trick?
Numbers 8 tak multiply hote hain: CD8×MHC-I=8, CD4×MHC-II=8
Antibodies ek intracellular virus se kyun nahi lad sakti?
Antibodies sirf free/extracellular antigen se bind karti hain; ye cells mein enter nahi kar sakti, toh T cells zaroori hain
Kaun sa lymphocyte HIV destroy karta hai, jo dono immune arms collapse kar deta hai?
CD4 helper T cells
B cell par antigen receptor ka naam aur T cell par antigen receptor ka naam batao.
B cell = BCR (membrane-bound antibody); T cell = TCR
Recall Feynman: ek 12-saal ke bacche ko explain karo
Sochon germs chor hain. Kuch chor khuli sadak par daud rahe hain (matlab germs tumhare blood mein float kar rahe hain). B cells woh guards hain jo khule mein daudne wale par chipchipe jaal (antibodies) fekte hain — lekin jaal tab bekar ho jaate hain jab chor pehle se kisi ghar ke andar ho. Toh humare paas T cells bhi hain, special police. Har ghar (cell) apni khidki par ek chhoti tray rakhta hai jo dikhaata hai andar kya hai. Agar ek T-cell tray par chor ka saman dekhe, toh ek type (CD8) chor ko rokne ke liye ghar jala deta hai, aur doosra type (CD4) woh captain hai jo sab ko radio karta hai aur kehta hai "zyada attack karo!". Do teams, do kaam: khule mein jaal, chhuppe hue ke liye police.
