Immunology | Medical Science Optional Notes for UPSC PDF Download

Innate vs Adaptive immunity

Cells of Immune System

The immune system comprises:

• Lymphocytes, responsible for recognizing antigens and initiating adaptive immune responses.
• Specialized antigen-presenting cells (APCs), tasked with capturing and presenting microbial and other antigens to lymphocytes.
• Effector cells, whose primary function is to eliminate microbes and other antigens.

Lymphocytes:

• Constitute 20-45% of differential leukocyte count (DLC).
• Number approximately 10¹².
• Small, round cells with a spherical nucleus.

Lymphocyte Recirculation

There is a continuous movement of lymphocytes through the bloodstream, lymph, and lymphatic organs/tissues. T cells predominantly constitute the recirculating cells, while B cells tend to exhibit a more stationary behavior.

Cluster of Differentiation

Several surface antigens or markers on lymphocytes and other leukocytes have been identified using monoclonal antibodies. These markers provide insights into the cell's stage of differentiation and functional properties. Currently, over 150 CD markers have been recognized, including:

• CD4 (T helper/inducer) and CD8 (Cytotoxic/suppressor)
• CD3, specific to T cells
• CD1, found in thymocytes/Langhans cells
• CD19/surface Ig, associated with B cells
• CD16/56, indicative of Natural Killer cells

MHC-the peptide display system of adaptive immunity

The human major histocompatibility complex (MHC), referred to as the human leukocyte antigen (HLA) complex, is comprised of a group of genes located on chromosome 6.

Additional proteins within the MHC locus, termed "class III molecules," encompass complement components (C2, C3, and Bf) as well as the cytokines tumor necrosis factor (TNF) and lymphotoxin. It's important to note that these molecules are not part of the peptide display system.

MHC-Types

MHC Restriction

Within each individual, T cells exclusively identify peptides presented by the MHC molecules unique to that person. These particular MHC molecules are the ones T cells typically encounter. This phenomenon is referred to as MHC restriction.

CD4 vs CD8

Th1 vs Th2

Other types of T cells

Antigen Presenting Cells

Dendritic Cells:

• Interdigitate dendritic cells, such as Langhans cells, are strategically positioned beneath epithelial layers to capture and present antigens to T cells.
• Plasmacytoid DCs, found in the blood and lymphoid organs, play a role in producing the major antiviral cytokine Interferon type I.
• Follicular dendritic cells (FDCs) reside in the germinal centers of lymphoid follicles in the spleen and lymph nodes. They enhance secondary antibody responses by trapping antigens bound to antibodies and complement, presenting them to activated B-lymphocytes in lymphoid follicles.

Macrophages:

• Macrophages ingest microbes and present antigenic peptides to T lymphocytes, contributing to cell-mediated immunity.

B Cells:

• B cells serve as antigen presenters to helper T cells and receive signals that stimulate antibody responses to protein antigens.

Effector Cells

Humoral And Cell Mediated Immunity (CMI)

• The type of immune response is contingent upon whether the lymphocyte is a B or T cell.
• T cells initiate cell-mediated immunity (CMI), whereas activated B cells generate antibodies, contributing to humoral-mediated immunity.

Cell Mediated Immunity (CMI)

Antibody mediated Immunity (Humoral)

Immunology-Repeats 

1. What are Immunoglobulins? Classify Immunoglobulins. Describe their role in host defense against communicable diseases. What are the modes by which immunoglobulins act on antigens? (2010) 
2. What is the mechanism involved in Type I hypersensitivity reaction? What types of agents can induce it? Describe the laboratory evaluation and management of allergic reactions. (2011)
3. Briefly describe various cells of immune system. Discuss classification systems to differentiate lymphocytes. Discuss cell-mediated immunity. (2012) 
4. Discuss the role of Natural Killer (NK) cells and Antibody Dependent Cytotoxic Cells (ADCC). (2014)
5. What are the features of innate and acquired immunity? What is the mechanism of action of immunoglobulins? (2015) 
6. Define and classify hypersensitivity. Describe type I hypersensitivity. (2015) 
7. Define immunological tolerance and discuss its role in autoimmunity, with one example. (2017)
8. Write short note on Monoclonal antibody and its application. (2018) 
9. Write short notes on Interferons and their uses. (2018) 
10. Briefly describe various cells of immune system. Discuss classification systems to differentiate lymphocytes. Discuss cell-mediated immunity. (2012) 
11. What are the features of innate and acquired immunity?