Question

1. Why is complement considered a part of Innate Immunity? Is this the only form of immunity it is part of - why or why not?

2. Describe the process of complement activation.

3. Pick one of the possible outcomes complement may have and describe the outcome.  

4. Why is more growth seen with the heat-inactivated plates?

5. What might it mean if, upon comparing Plate Set 1 (PS1) and Plate Set 2 (PS2) for the soil sample, they differ significantly in the numbers of colonies produced?

Answer 1

1. Complement system is basically an arm of immunity that contain many soluble proteins. These proteins can act long distance as they travel along with the blood- like hormones. Complement proteins are mainly synthesised in the liver but many other cells like macrophages, neutrophils, dendritic cells and T cells also synthesise complement proteins.
Complement proteins act at the site of breach by a pathogen to assemble the components of innate immunity.
complement systems is a part of innate immunity because it is a quick, non specific and short lived response to a foreign body. Complement proteins recognise Pathogen Associated molecular pattern ( PAMPs) and gets activated. Also, two of the pathways of complement activation does not require antibody making it an innate immune response.
Complement proteins acts are chemoattractants, opsonising agents as well as inflammatory proteins.

Complement is also a major effector mechanism of adaptive immunity. T helper cells when activated release various cytokines to induce B cell activation and to activate other immune responses. Hence, complement proteins acts in innate as well as adaptive immune responses.

2. There are three pathways of complement activation. All of these pathways include cleavage of complement proteins into subunits that further cleave other proteins into functional subunit which ultimately assemble to form a complex called Membrane attack complex ( MAC).

The subunits are denoted as 'a' or 'b' and complement protein is called C1, C2 , C3 etc. (subunit a of complement C3 is written as C3a)

Below is an overview of all the three pathways of complement activation. If you have any queries regarding it please ask in comment section.
these pathways seems a bit confusing but don't need to remember everything just kept in mind the following points.
1. in classical pathway complement is activated by antigen - antibody complex and it involves C1 complement to initiate.
2. in lectin pathway Membrane binding lectin (MBL) recognises mannose residue on the bacterial membrane and this pathway is independent of antibody.After initiation it also utilises C2 and C4 proteins to form MAC.
3. In alternative pathway C3 complement resides on the surface of microbes and undergo activation to produce C3b which further uses factor D to form C5 convertase and MAC.
4. All these pathways ultimate leads to the formation of membrane attack complex that binds to the pathogen membrane and drills a hole in it to disrupt it.
5. complement pathways can use antibodies or directly recognise PAMPs.

classical pathway obal abone denoted that the complex is activated Antigen Antibody CL → Activated CI complex cab C2 (4b2a C4b23b C46 C4 Сча را csa I cab CS Lectin athi micabbial wall MBL C5 C5b→→→→566789 (MAC) Activated CL-like complex Alternative Factor D microones pathway szaface C36 ✓ C36B5 → C36135 36 C3 n Ba

3. One possible outcome of complement activation is formation of Membrane attack complex (MAC). As described above it is formed by various complement subunits- C5b6789. This MAC can lyse a large number of pathogens from bacteria to viruses. MAC forms a channel like structure on the membrane of pathogen. Since ions and small molecules can diffuse freely inside the cell , the osmotic stability is ruined and the cell dies. The structure of MAC is shown below

4. Heat inactivation is done to inactivate the complement. Since complement is composed of proteins which gets denatured at high temperatures. When you heat inactivate a plate, you kill off an important innate immune system - the complement system. Hence, immune compromised state will be achieved which will lead to more growth of bacteria and pathogens.

c5b64 C8 I Baderial се с И Рөс Membrane attack complex (csge )

5.please provide information on plate set 1 and plate set 2 in the comment sections.