4. Adaptive Immunity (Part 1)

Two major groups of pathogens animals defend against

Pathogens outside body (bacteria, viruses, fungi, protozoa, helminths) and inside body (virus-infected cells, cancer cells)

Adaptive immune system is divided into these two branches

Humoral (antibody-mediated) and Cell-mediated

Humoral immunity primarily involves

B cells and antibodies; targets free infectious agents

Cell-mediated immunity primarily involves

T cells; targets cell-associated antigens (e.g., infected/cancer cells)

Lymphocytes are predominant in these organs

Spleen, lymph nodes, thymus, and blood

Humoral immunity definition

Immune response involving antibodies found in body fluids (humors)

Cell-mediated immunity definition

Immune response not involving antibodies; uses activated phagocytes and cytotoxic T-cells

First step in antigen presentation

Macrophage engulfs pathogen, processes it, displays antigen fragments on its surface

Antigens are presented on macrophage surface using

this molecule

The number of immune cells mobilized is proportional to

this

In embryos, lymphoid cells are initially made in

Omentum, then liver

In older fetuses/adults, lymphoid cells are made in

Bone marrow

Three primary lymphoid organs

Thymus, Bursa of Fabricius (birds), Peyer's Patches

Function of primary lymphoid organs

Regulate production and differentiation of lymphocytes; do NOT respond to antigens

Thymus location and function

Anterior mediastinum/neck; differentiates and matures T lymphocytes; largest in newborns, atrophies at puberty

Bursa of Fabricius is found in

this animal class only

Peyer's Patches location

Mucosa of jejunum and ileocecum in newborns; jejunal patches persist for life

Secondary lymphoid organs include

Lymph nodes, spleen, bone marrow

Main function of secondary lymphoid organs

Trap and present antigens to lymphocytes; rich in antigen-presenting cells (macrophages, dendritic cells)

Dendritic cells originate here

Bone marrow

Dendritic cell function

Capture and present antigen to T-cells in lymphoid tissue; have cytoplasmic "feet"

Lymph node function

Filter lymph to trap antigens from tissues before they reach systemic circulation

Spleen has these two anatomical/functional sections

Red pulp (RBC storage/filtration) and White pulp (immune response, lymphocyte-rich)

MALT and GALT are part of

this system

Immunogenicity definition

Degree to which a substance stimulates a specific immune response

Four physiochemical parameters affecting immunogenicity

Size, Stability, Degradability, Complexity

Larger antigen size makes it

this

Epitope definition

Specific site on an antigen where an antibody binds; also called antigenic determinant

Cross-reaction basis

Immune response to one pathogen mistakenly reacts to a different molecule sharing the same epitope

Hapten definition

A small molecule that is not immunogenic alone but becomes so when attached to a larger carrier molecule

Example of hapten-carrier reaction

Flea saliva antigen (hapten) binds to skin collagen (carrier), triggering flea allergy dermatitis

Self-antigens are normally

this

Major Histocompatibility Complex (MHC) molecules are critical for

this

Histocompatibility antigens are found on

this

Class I MHC molecules are expressed on

this

Class II MHC molecules are expressed on

this

Four major antigenic structures on bacterial surface

Cell wall, Pili, Capsule, Flagellae

Viral component that is highly antigenic

Viral capsid (protein coat)

How viruses evade humoral immunity

By hiding inside host cells, protected from circulating antibodies

How infected host cells become targets for immune system

Viral infection alters host cell MHC presentation, making the cell membrane antigenic