CLS 1113 Introduction to Clinical Laboratory Practices

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CLS 1113Introduction to Clinical Laboratory
Practices

• Unit 4
• The Lymph System and
• Immunoglobulins

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The Lymph System

• Lymphocytes are wholly responsible for the
  specific immune recognition of pathogens, thus
  initiating acquired immunity.
• Lymphocytes make up 20-40 of circulating WBCs.
  
• Lymphocytes are derived from bone marrow stem
  cells
• T cells develop in the thymus
• B Cells develop in the bone marrow

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Primary Lymph Organs

• Bone Marrow
• Main source of hematopoietic cells - antigen
  independent lymphopoiesis
• Largest tissue in the body
• B lymphocytes differentiate
• Thymus
• Flat bilobed organ in the chest cavity.
• Increases in size until puberty and then
  atrophies.
• T lymphocytes differentiate

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Secondary Lymph Organs

• The secondary lymph organs include
• Spleen, lymph nodes, tonsils, and the appendix
• Upon differentiation the T and B cells migrate to
  secondary lymph organs Recirculate
• Approx 1-2 total Lymph / hour
• Because lymphocytes are very specific for certain
  antigens, they must circulate to increase the
  chances of detection.
• Antigen dependent lymphopoiesis

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Secondary Lymph Organs

• Spleen
• Red Pulp Culling of senescent red blood cells
• White Pulp Lymphoid tissue filter
• Primary Follicle unstimulated B Cells
• Lymph Nodes
• Serve as central collecting points for lymph
  fluid from tissues
• Filtration Phagocytosis, antigen processing and
  generation of B Cell memory
• Secondary Follicle Antigen stimulated
  proliferating
• B cells

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Secondary Lymph Organs

• Tonsils
• Respond to respiratory and alimentary tract
  pathogens
• Potential site for Antigen contact
• Appendix
• Potential site for Antigen contact

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Surface Markers on Lymphs

• Lymphocytes express many molecules (proteins)
  called Markers on the cell surface which are
  used to differentiate cell populations, etc.,
  i.e. B and T cells
• Systematic Nomenclature CD (Cluster of
  Differentiation)
• Groups or Clusters of Monoclonal antibodies that
  bind to a specific marker.

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CD Markers

• CD4 is the Marker expressed on T helper cells.
  T helper cells are very active in our cell
  mediated immunity.
• The HIV virus attaches to the CD4 markers on T
  cells
• (route of entry) that is why HIV patients
  progressively lose their immune function.
• CD8 cells are T suppressor cells / cytotoxic T
  cells. CD8 cells help keep our immune system
  under control and help fight tumors (cytotoxic).
• The CD markers on our white cells change as the
  cell matures helping us define maturity or age of
  the cells.

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Antibody Structure and Function Immunoglobulins

• When B cells are stimulated by antigen they
  undergo differentiation and produce Antibodies
  a.k.a. Immunoglobulins (Ig)
• Glycoproteins found in the serum
• Five classes with names based on electrophoretic
  pattern IgG, IgM, IgA, IgD and IgE
• These differ in size, charge, amino acid
  concentration and carbohydrate content.
• Humoral Immunity

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Immunoglobulin Structure

• All Igs are made up of a four chain polypeptide
  unit
• Two large chains HEAVY (H) Chains
• Two small chains LIGHT (L) Chains
• Two types ? (kappa) and ? (lambda)
• FAB Fragment Antigen Binding
• Portion of the antibody that binds to the antigen
• Fc Fragment crystalline
• Portion of the antibody that remains constant

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IgG

• 75 of Serum Immunoglobulins
• Monomer 2 Heavy Chains 2 Light Chains
• Cross Placental Barrier
• Number of Sub-Classes
• Complement Activation
• Optimum Temperature
• Predominant Ig in SECONDARY immune response
• Table 5-1

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IgM

• 10 of total serum Immunoglobulin
• Pentamer
• 10 Heavy 10 Light Chains
• Includes also a J (joining) chain
• Predominant Ig in Primary immune response
• Complement activation
• Optimum Temperature
• Cross Placental Barrier
• Presence on Lymphocyte membrane

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Immunoglobulins

• IgA
• Location- body secretions
• Dimer
• Contains a secretory component
• J Chain
• IgE
• Low plasma concentration
• Bound to basophils and mast cells
• Triggers release of histamines

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Immunoglobulins

• IgD
• Complete function unknown
• It is speculated that IgDs play a role in keep
  in the immune system under control (suppression).

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