Site of infection

Microbes may be found in

1. Extracellular: attached to the human cells on epithelial surface like cholera or not attached to human cells( in interstitial spaces, blood and lymph ) like staphylococcus aureus.

2. Intracellular: present free in the cytoplasm like viruses or enclosed inside vesicles like mycobacterium of TB.

Functions of the complement proteins:

1- Lysis of the microbes by MAC

2- Promotion of phagocytosis of microbes (oposonization) by C3b.


3- Induction of inflammation by C3a & C5a.

4- Attraction of the inflammatory cells to the site of infection by C3a & C5a.

5- Clearance of immune complexes by phagocytes by CR1 & C3b.

How RBCs help in immunity?

CR1 expressed on erythrocytes aids in the transport of immune complexes to the liver and spleen for degradation by phagocytes.

حسب رأيي الدكتورة ما جاوبت عليه

C1 inhibitor (C1INH) is a protease inhibitor that displaces active C1r2s2 from C1q and
inhibits MASP-1 and MASP-2 of the lectin pathway.

Also called C1q binding protein

It is similar to C4.

👉It produced by the MICROBES.

👉Its deficiency lead to HEREDITARY ANGIOEDEMA ➡ increase activation of classical and lectin pathways ➡ over immune response.

👉Gram positive bacteria can't be killed by MAC so we use C3b to kill it by phagocytosis.

👉Because CR1 which present on the surface of phagocytes has high affinity for C3b and C4b which coat antigens .

👉C3b deficiency ➡ immune complex diseases due to deposition of immune complexes which not cleared by C3b.
👉Also lead to increase infection of capsulted bacteria.

👉Adhesion mediated by CR3 & CR4.
👉Oposonization mediated by CR1 & CR3.

1-Tickover activation
active in HEALTHY people.
2- Membrane bound cascade active only in INFECTED people.

👉mannose-binding lectin (MBL) is a protein produced by hepatocytes .

👉MAC Affect more gram NEGATIVE bacteria.

👉CR1 affect more grame POSITIVE bacteria.

👉Lysozymes affect more gram POSITIVE bacteria.

👉Defensins affect both gram POSITIVE & NEGATIVE bacteria.

👉Why the RNase & protein kinase which produced by type 1 interferon (secreted by virus infected cells) don't degrade our RNA & proteins in cells which are not yet infected?

👉Because they are secreted as inactive but they will be active by presence of virus ➡ degradation of our &virus RNA 😔.

Acute phase proteins (Binding proteins)

They are synthesized by liver cells in response to IL-6 , lL-1 &TNF.

👉Why Defensins degrade microbial cells but not our cells?

👉Because Defensins inhibited by presence of cholesterol on our cells which not present on microbes.

👉Why lysozymes degrade microbial cells but not our cells?

👉Because Lysozyme degrades the peptidoglycan layer in the bacterial cell wall which not found in our cells.

👉Why broad spectrum antibiotics which kill normal flora lead to increase bacterial infection?

👉Due to 1- increase the attachment site for pathogenic bacteria which was occupied by normal flora.
2- Decrease of monolactam & colicins which was secreted by normal flora to kill pathogenic bacteria.

👉Bacteria which can invade the intact skin is Bacteria which cause syphilis ( trypanosoma pallidum) .

Why there is a decrease in immune response in pregnancy?

حتى لا يحدث rejection of baby.

Why Vaccines are given IM, SC, oral but not IV ?

Because a given dose of antigen may elicit no detectable response when injected intravenously but may elicit a strong immune response if injected intradermally or subcutaneously due to
● Slow removal of the antigen ➡ increase the contact between antigen & immune system .
● Presence of antigen-presenting cells (APCs).

👉Why we prefer Vaccines with adjuvants ?

👉Because Adjuvants are agents which when administered along with an antigen enhance the specific immune response.

👉CD35 (CR1) is a membrane bound co-factor which inhibit complement formation on human cells .

👉CD55 is a decay-accelerating factor which inhibit complement formation on human cells but not microbes .

👉CD59 is The major membrane inhibitor of MAC formation on human cells by inhibition of C9 polymerization.

All of them found on human cells but not microbes.

👉CD56 is a receptor present on the surface of Natural Killer cells (NK cells).

Why MHC class ll Closed by invariant chain ?

عشان يمنع ارتباطه ب ال intracellular pathogens.
لانه وظيفته يرتبط ب ال extracellular pathogens.

👉B cells , macrophages & Dendritic cells are called professional cells what the deference between them ?

👉B cells is specific (every cell against one microbe).
👉macrophages & Dendritic cells are non specific.