45 Difference Between Immunoglobulins and Complement Proteins

A vital part of the immune system, immunoglobulins and complement proteins have different functions in protecting the body from infections and sustaining immunological responses.

B lymphocytes (B cells) create the specialized proteins known as immunoglobulins (Ig), also referred to as antibodies, in reaction to the presence of foreign substances such as antigens. Four protein chains, two identical heavy chains and two identical light chains, make up the Y-shaped structure of antibodies. The Y-shaped antibody molecule has a region on each arm that can recognise and bind to a particular antigen.

Immunoglobulins fall into five basic categories, each with a distinct set of properties:

The first antibody to be produced in response to an infection is IgM. It is essential for the pathogens to agglutinate (clump) and for the complement system to be activated.
IgG: The most prevalent class of antibodies, IgG protects babies by neutralizing pathogens, encouraging phagocytosis (the immune system’s devouring of pathogens), and facilitating transit across the placenta.
IgA: Predominantly present in physiological fluids including saliva, tears, and mucous secretions, IgA offers localized immunity on mucosal surfaces and keeps infections out of the body.
IgE: This group of antibodies is linked to allergic reactions and parasite defense. Allergy symptoms are brought on by IgE, which causes mast cells to produce histamine.
IgD: Although its precise role in B cell activation is not fully understood, IgD can be located on their surface.

Over 30 proteins make up the complement system, which collaborates to strengthen the immune response to infections. Both the innate and the adaptive immune systems contain complement proteins, which have a variety of functions.

Complement proteins can coat infections with chemicals that promote phagocytosis, a process known as poisoning. Opsonization is the process that makes it simpler for immune cells to detect and absorb viruses.

Complement activation causes the release of inflammatory mediators such as cytokines, which draw immune cells to the infection site and cause inflammation.
Cell lysis: Complement proteins can assemble into a membrane attack complex (MAC), which breaks pores in pathogens’ membranes and kills them.
Immune complexes (antigen-antibody complexes) are cleared from circulation with the help of complement proteins.
Enhancement of Adaptive Immune Response: Complement activation can also help to activate B cells and increase the generation of antibodies.

S.No.	Aspects	Immunoglobulins	Complement Proteins
1	Definition	Antibodies produced by B cells	Serum proteins in the immune system
2	Classification	IgG, IgM, IgA, IgD, IgE	C1-C9, factors B, D, P, H, and I
3	Synthesis Location	Mainly in plasma cells	Various cell types, mainly liver
4	Structure	Y-shaped with heavy and light chains	Composed of multiple proteins
5	Antigen Recognition	Bind directly to antigens	Do not directly bind antigens
6	Specificity	Highly specific to antigens	Non-specific activation
7	Effector Functions	Opsonization, neutralization, complement activation	Complement cascade activation
8	Molecular Weight	Smaller, around 150 kDa	Larger, varying from 25 kDa to 200 kDa
9	Role in Immunity	Adaptive immune response	Part of innate immune response
10	Presence in Serum	Present as soluble proteins	Present as soluble proteins
11	Antibody Classes	IgG, IgM, IgA, IgD, IgE	C1q, C1r, C1s, C2, C3, C4, C5, C6, C7, C8, C9
12	Activation	Antigen binding activates them	Activation by enzymatic cascades
13	Antigen Binding Sites	Variable and constant regions	No antigen-binding sites
14	Secretion	Secreted by plasma cells	Synthesized by liver and other cells
15	Half-life	Longer half-life (days to weeks)	Shorter half-life (hours to days)
16	Opsonization	Yes	No
17	Effector Enzymes	No	Yes (e.g., C3 convertase)
18	Receptors	Fc receptors on immune cells	Receptors on various cell types
19	Memory	Contribute to immunological memory	No memory function
20	Primary Function	Adaptive immune response	Enhance immune responses
21	Clonal Selection	Involved in clonal selection	Not involved in clonal selection
22	Secretion Regulation	Regulated by B cell activation	Constitutive secretion
23	Role in Autoimmunity	Can contribute to autoimmune diseases	Not directly implicated in autoimmunity
24	Diversity	High diversity due to variable regions	Limited diversity
25	Isotypes	Different isotypes (IgG1, IgG2, etc.)	Different factors (C1, C2, etc.)
26	Activation Trigger	Antigen recognition	Pathogen surface components
27	Opsonization Mechanism	Coating pathogens with antibodies	No opsonization
28	Crosslinking	Can crosslink antigens	No crosslinking
29	Role in Humoral Immunity	Central to humoral immunity	Enhance humoral immunity
30	Role in Cell Lysis	Limited role in cell lysis	Crucial in cell lysis
31	Role in Inflammation	Limited role in inflammation	Can contribute to inflammation
32	Role in Immune Complexes	Form immune complexes	Not involved in immune complexes
33	Complement Activation Pathway	Not involved in complement activation	Initiates complement cascade
34	Antigen Recognition Timing	Slower recognition of antigens	Rapid recognition of pathogens
35	Role in Allergic Reactions	Can trigger allergic reactions	Not involved in allergies
36	Role in Phagocytosis	Enhances phagocytosis	No direct role in phagocytosis
37	Antibody Production Regulation	Regulated by antigen exposure	Constitutively present
38	Role in Antigen Presentation	Antigen presentation via MHC	No role in antigen presentation
39	Role in Immune Memory	Essential for immune memory	No role in immune memory
40	Effect on Microbes	Neutralizes and opsonizes microbes	Lyses microbes and triggers inflammation
41	Role in Self vs. Non-self Recognition	Discriminate between self and non-self	No role in this discrimination
42	Association with Diseases	Implicated in autoimmune diseases	Complement deficiencies lead to infections
43	Activation Mechanism	Binding to specific antigens	Activation by proteolytic enzymes
44	Role in Antibody-Mediated Immunity	Central role in this type of immunity	No direct role in this type of immunity
45	Role in Adaptive Immune Response	Key players in adaptive immunity	Limited involvement in adaptive immunity

Frequently Asked Questions (FAQs)

Q1.What's an immunoglobulin's structure?

The Y-shaped structure of immunoglobulins is made up of two heavy chains and two light chains. Disulfide bonds hold these chains together. Antigen-binding sites, which are the tips of the Y-shaped structure, are in charge of binding to particular antigens.

Q2.What function do IgG antibodies serve?

The most prevalent and adaptable antibodies are IgG antibodies. By eliminating toxins, boosting phagocytosis, and crossing the placenta to safeguard fetuses, they offer long-lasting protection.

Q3.Describe opsonization?

Complement proteins wrap infections to make them more recognisable to phagocytic cells like macrophages and neutrophils. This process is known as opsonization. As a result, pathogen engulfment and killing are more effective.

Q4.The membrane attack complex (MAC) is what, exactly?

The complement proteins that constitute the membrane assault complex cooperate to puncture the membranes of the target cells, leading to cell lysis.

Q5.Complement proteins: Are they a component of innate or acquired immunity?

Although they can interact with and improve the adaptive immune response as well, complement proteins are largely a component of the innate immune response.