Lymphatic And Immune Systems -nsu

Histology 9 Gregory Rodocker NSU Class Taken: Spring 2009

The Immune System and Lymphoid Organs 

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By distinguishing self from non-self, the immune system protects the body from external microorganisms and substances that may damage the body This includes protecting the body from internal invaders such as cancer cells. 

Unfortunately, the immune system can turn against the body and produce autoimmune diseases

Types of Immunity 

Innate/passive  

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Does not require exposure to antigen Includes skin, mucous membranes, species specific disease

Acquired/active   

Requires exposure to antigen Has a memory Both cellular and humoral

The Immune System and Lymphoid Organs 

Composed of 

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Organs such as the lymph nodes, thymus, and spleen Cells throughout blood and CT   

Lymphocytes Granulocytes Antigen presenting cells

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This illustration shows the wide distribution and multiple locations of immunocompetent tissues.

Lymphocytes *stopped here* 

B cells – 5-10 %    

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Bone marrow derived Plasma cells secrete antibodies 150,000 IgM on each cell specific to one antigen Memory cells

T cells – 65-75 %   

Thymus derived Helper, cytotoxic and memory cells (NK lymphocytes – 10-15 %)

The two aspects of the immune response

Immunobglobulins  

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IgG – most abundant; crosses placental barrier; activates complement IgA – dimeric secretory Ig; mucous secretions, tears, colostrum, saliva and reproductive tract IgM – pentameric, surface of B lymphocytes; activates complement IgE – surface of mast cells and basophils; trigger allergic reactions IgM - surface of B lymphocytes; B lymphocyte development

MHC 

Major Histocompatibility Complex 

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Integral Proteins in two classes  

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How body tells self from non-self MHC-I (on all cells) MHC-II (on antigen presenting cells)

Also known as HLA or Human Leukocyte Antigen (originally found in humans on WBC’s)

Organ Transplantation 

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Autografts – when tissue or organ taken from the person receiving the transplant Isograft – when organ or tissue taken from an identical twin Homograft – when organ or tissue from same species Heterograft – when organ or tissue taken from a different species

Organ Transplantation 

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Autografts and Isografts usually work well as MHC-I match Homografts and heterografts are problematic  

MHC-I does not match Attack primarily by cytotoxic T-cells and natural killer (NK) T-cells

Graft vs. Host Disease (GVHD) 

Occurs when immunocompetent donor tissue attacks the tissues of the host. 

Acute GVHD describes a distinctive syndrome of dermatitis, hepatitis, and enteritis developing within 100 days of allogeneic hematopoietic cell transplantation (HCT). Chronic GVHD describes a more diverse syndrome developing after day 100.

Stem Cell Source 

The different types of stem cell transplants are named from the origin of the stem cells:  

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autologous - stem cells harvested from self allogeneic - stem cells harvested from donor (following reduced for full intensity therapy) syngeneic - stem cells harvested from identical twin cord blood - stem cells from saved cord blood, from self or donor

Thymus  

Located in the mediastinum Divided into lobules (by extensions of CT capsule) that each have an outer cortex and an inner medulla 

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Cortex is T lymphocytes, epithelial reticular cells and macrophages (stains more darkly as contains more small lymphocytes Medulla contains fewer lymphocytes and more epithelial reticular cells

Cortex

Epithelial ReticularCells

Lymphocytes

Hassall’s Corpuscles Cortex Medulla

Hassall’s corpuscles – degenerating centers, may calcify, unknown role.

Connective Tissue Capsule of Thymus

Artery

Vein

T Cell terminal differentiation and selection 

The thymus is the site of lymphocyte division followed by apoptosis of 95% of the cells 

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Either they do not react to any antigen and are therefore useless or React with self-antigens and would be self destructive (autoimmune diseases) i.e. clonal deletion

Thymus involution 

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Thymus is largest at birth and begins to “involute” at puberty At left is the thymus from an elderly individual and it is mostly adipose cells

Factors influencing the Thymus 

Paracrine factors in the Thymus 

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Thymosine –α, thympoietin, thymolin, thymus humoral factor

Other hormonal effects 

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Adrenocorticosteriods inhibit as do ACTH from the pituitary Androgens and estrogens also inhibit as well as trigger involution at puberty

Lymph nodes 

Inline filters of the lymph system 

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All tissue collected lymph is filtered by at least one node before lymph returns to the circulation

Largest numbers are in the groin, armpits, along the great vessels of the neck, and in the thorax and abdomen and in the mesenteries

Hilum

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Nature ReviewsI immunology

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Picture of lymphocytes become mature.

Spleen 

Largest accumulation of lymphoid tissue in the body 

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Characterized by areas of white pulp and red pulp CT capsule that extend trabeculae into the body of spleen

White and red pulp  

White – mostly T and B lymphocytes Red – reticular cells (reticular type III collagen fibers), macrophages, T and B cells, plasma cells, erythrocytes, platelets and granulocytes

Mucosa-Associated Lymphoid Tissue: MALT 

The digestive, respiratory and genitalurinary tracts are common sites of microbial invasion 

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Hence, there are special aggregates of lymphoid tissues in their mucosa and submucosa –(tolinsles & priors patches)are these. Sometimes these aggregates are large as tonsils and Peyer’s patches

MALT 

AKA (subcategories)      

GALT – gut BALT – bronchial NALT – nose SALT – skin VALT – vascular CALT - conjunctiva

Tonsils 

Depending on the location they are called the   

Palatine Pharyngeal (Adenoids) Lingual

1. Adenoids (pharyngeal tonsil) 2. Palatine tonsils (single) 3. Lingual tonsils

Tonsilar Crypts