Lecture 7: White Blood Cells

Question 1

What are the 2 types of Normal leucocytes?

Answer 1

White Blood Cells

Leucocytes (white cells) may be divided into two broad groups: phagocytes and lymphocytes. Normally only m_ature phagocytic cells and lymphocytes_ are found in the peripheral blood.

Phagocytes include:

• Granulocytes
  
  • Neutrophils (also known as polymorphs or polymorphonuclear leucocytes)
  • Eosinophils
  • Basophils
• Monocytes

Lymphocytes include:

• B and T cells
• NK cells

Question 2

What ar ethe function of both pathocytic cells and lymphocytes?

Answer 2

The function of both phagocytic cells and lymphocytes is to protect body against infection.

This function is closely connected to the production of two sets of proteins in body – immunoglobulins and complement.

Question 3

Describe the Morphology of Neutrophils

Answer 3

Morphology

Neutrophils represent over 90% of the circulating granulocytes, 75% normal leucocytes

• They are large (10-15µm in diameter)
• They have a characteristic dense nucleus consisting of 2-5 lobes and a pale cytoplasm with irregular outline and containing many fine pink (azurophilic) or violet-pink granules

Question 4

When looking at blood tests, what are we actually measuring?

Answer 4

Total white cell count: L (absolute count)

Red cell: (talk about Haemoglobin not RBC count)

Question 5

Describe the Neutrophil Development

Answer 5

Neutrophil Precursors (Myeloid Development)

These do not normally appear in peripheral blood but are present in marrow.

7-10 day maturation in the marrow

When released, it circulates from 6-10 hours, then goes into tissues where they perform phagocytic functions (show how proliferative the bone marrow is)

• The earliest recognisable precursor is myeloblast.
  
  • Cytoplasm is basophilic and no cytoplasmic granules are present.
• Myeloblasts give rise by cell division to promyelocytes.
• These cells give rise to myelocytes.
  
  • They have specific or secondary granules.
• The myelocytes give rise by cell division to metamyelocytes.
  
  • They ar_e non-dividing cells_, which have an indented or horseshoe-shaped nucleus.
• Metamyelocytes mature to band neutrophil then fully mature segmented neutrophil

Question 6

Describe the Regulation of Granulopoiesis

Answer 6

Granulocyte-colony stimulating factor (G-CSF)

Increases granulocytes proliferation, increases maturation, increases the release of segmented and band neutrophils into the blood.

Question 7

Describe the functions of the neutropbhils

Answer 7

It is primarily involved in i_nfection response_, which has three phases (chemotaxis, phagocytosis, and killing via oxidative or non-oxidative).

• Chemotaxis (cell mobilisation)
  
  • Phagocyte is attracted to bacteria or site of inflammation probably by chemotactic substances released from damaged tissues (leucocytes and platelets), bacteria (endotoxin), prostaglandins, products of fibrinolytic and kinin generating system and components of complement pathway.
  • Neutrophils are able to move between contiguous endothelial cells be inserting a pseudopod and subsequently penetrating the basement membrane.
• Phagocytosis
  
  • Foreign material (e.g. bacteria, fungi, etc.) or dead or damaged cells of host’s body are phagocytosed.
  • Recognition of a foreign particle is aided by opsonisation with immunoglobulin or complement, since both neutrophils and monocytes have surface receptors for Fc fragment of immunoglobulins and for C3 and other complement components.
• Killing (oxidative/oxygen-dependent and non-oxidative/oxygen-independent)
  
  • In oxygen-dependent reactions, superoxide and hydrogen peroxide (H2O2) are generated from oxygen and NADPH or NADH. In neutrophils, H2O2 reacts with myeloperoxidase and intracellular halide to kill bacteria (superoxide (O2-) may also be involved).
  • In non-oxidative microbicidal mechanism, it involves decreased pH within phagocytic vacuoles into which lysosomal enzymes are released. Lactoferrin (iron binding protein present in neutrophil granules) is bacteriostatic by depriving bacteria of iron.

Question 8

What are 3 clinical cases that are relevant for neutrophils?

Answer 8

Neutrophil leucocytosis is features of bacterial infection, inflammation, trauma, acute blood loss.

• Patients present i_ncrease in neutrophil_s,
• May be associated with “left shift” (more immature forms in the blood).

Neutropenia (low neutrophil count) causes include congenital, drug effect, immune, cyclical, viral infection.

• Patients present with recurrent infection, mouth ulcers, fevers (febrile neutropenia).

Neutrophil function defects are rare.

Question 9

What is this?

Answer 9

Neutrophil

Question 10

What is this?

Answer 10

Eosinophil

Question 11

What is this?

Answer 11

Basophil

Question 12

What is this?

Answer 12

Monocyte

Question 13

Describe the morphology of Monocytes

Answer 13

Morphology

These are of variable appearance.

• It is usually larger than other peripheral blood leucocytes (15-20µm in diameter).
• It possesses a large central oval or indented nucleus with clumped chromatin.
• Abundant cytoplasm stains pale blue/gray and contains many fine vacuoles giving a ground-glass appearance.
• Cytoplasmic granules are also often present.
• Very low count (less than 10% of total WBC count)

Question 14

Describe the development of Monocytes

Answer 14

Monocyte Development

Monocyte precursors in marrow (monoblasts -> promonocytes) are difficult to distinguish from myeloblasts and monocytes.

1. CFU-GM
2. Monoblast
3. Promonocyte
4. Monocyte

Question 15

What are the kinetics of monocytes?

Answer 15

1. Monocytes circulates for 1-3 days
2. Enter tissues and transform into macrophage
3. Related cells throughout the body
   
   • Kupffer cells- liver
   • Alevolar macrophages
   • Langerhans cell skin
   • Microglial cell brain

Question 16

What are the functions of monocyte/macrophages?

Answer 16

1) Phagocytic functions

• Chronic infections, intracellular parasites e.g. TB
  
  • Chemotaxis
  • Opsoniation- receptors Fc and C3
  • Phagocytosis and ingestion
    
    • But seen more in chronic illnesses
  • Killing of ingested bacteria by fusion with monocytic lysosomal granules

2) Synthetic function

• Complement
• Interferon
• Cytokines e.g. TNF, IL1, growth factors
• Prostaglandins

3) Antigen presentation

• Present to T cells as part of the adaptive immune response

Question 17

What are the clinical relevance of Monocytes?

Answer 17

Monocytosis

Reactive monocytosis include chronic bacterial infections such as TB, osteomyelitis

Malignant monocytosis include acute myeloid leukaemia (monoblastic sybtype), _chronic myelomonocytic leukaemia (_CMML), myelodysplasia.

Question 18

Describe the morphology of eosinophils

Answer 18

These cells comprise 2-5% of blood leucocytes normally.

They are similar to neutrophils except cytoplasmic granules (red staining) are coarser and more d_eeply red staining_ and they usually have bilobed nuclei *.

Eosinophil myelocytes can be recognised but earlier stages are indistinguishable from neutrophil precursors (developmental stages similar to neutrophils).

Question 19

What are the functions of Eosinophils?

Answer 19

Eosinophils function much like neutrophils in that they have amoeboid motion and can _phagocytise bacteri_a, particles and other antigen-antibody complexes.

• They are attracted by eosinophil chemotactic factor of anaphylaxis ECF-A and histamine (both released from mast cells and basophils), other chemotactic products (released by bacteria and components of complement).
• They also bind parasites such as schistomulae (coated with IgG antibody), degranulate and release toxic protein (“major basic protein”).
• They also release histaminase and aryl sulphatase, which inactivate histamine and slow reacting substance of anaphylaxis (SRS-A) and dampen immediate (type I) hypersensitivity response.

Question 20

What is the clinical relevance of Eosinophils?

Answer 20

Eosinophilia (increased peripheral blood eosinophils) is seen in patients with allergic or hypersensitivity reactions (e.g. hayfever, asthma, drug reactions), parasitic infections.

Question 21

Describe the morphology of Basophils

Answer 21

Basophils are found in very small numbers in the circulation (0-2%) and are thus difficult to find in a routine blood film.

When seen, they appear with deep violet-blue granules over nucleus.

They have IgE binding sites

Basophils and mast cells are functionally related being of bone marrow origin.

Basophils predominantly exist in circulation, w_hile mast cells exist in tissues._

Question 22

What are the functions of Basophils?

Answer 22

Basophils and mast cells have I_gE attachment sites._

Granules include h_istamine, SRS-A, ECF-A._

Cross linking of IgE by allergen results in degranulation with histamine release, which mediates many of the s_ymptoms of allergy (type I hypersensitivity)._

Question 23

For the following cells, what are the type of infections they respond to, and what are the potential functional capabilities and responses to these infections?

Answer 23

See table

Question 24

Describe the development of Lymphocytes

Answer 24

Lymphocytes develop from pluripotent haematopoietic stem cells, located in adult bone marrow and in fetal liver.

Lymphocytes are matured from stem cells in p_rimary lymphoid organs (bone marrow and thymus) a_t a high rate (10⁹/day).

Many of these cells migrate via circulation and lymphatics into s_econdary lymphoid tissue (lymph nodes, spleen)._ Larger lymphocytes may also occur in peripheral blood (stimulated by antigenic challenge, e.g. viruses or foreign proteins).

Lymphoid tissue as a whole makes up 2% of total body weight. Circulating lymphocytes are ~20% total white blood cell count.

Question 25

Describe the Morphology of Lymphocytes

Answer 25

Circulating lymphocytes include 65-80% T cells, 5-15% B cells, NK cells (natural killer cells with larger cytoplasmic granules).

• B and T cells morphologically identical
  
  • At an ultrastructural level, T lymphocytes have few intracytoplasmic organelles, although a number of lysosomal enzymes can be demonstrated by cytochemical staining.
  • In peripheral blood, most B lymphocytes express IgM and IgD antibodies on surface membrane.
• They are identified by c_ell surface markers_, e.g. B cells with CD19, CD20, CD22; T cells with CD3 and either CD4 or CD8

Question 26

What are the functions of primary lymphoid organs?

Answer 26

Lymphoid cells have s_pecific immune respons_e (high degree of specificity involved in the recognition of non-self).

• B cells differentiate into plasma cells (antibody production) and memory B cells in peripheral lymphoid tissues.
• _T cells d_ifferentiate into CD4 positive T helper cells and CD8 positive T cytotoxic cells (both responsible for cell mediated immunity).

There are two broad classes of immune responses

• Humeral antibody responses which involve the production of antibodies which may circulate in the blood stream and bind to the antigen which induced them.
• Cell mediated immune responses which invoke the production of specialised cells that react with foreign antigens (mainly on the surface of host cells) and either kill them or induce other cells to destroy the antigen.

Question 27

Primary lymphoid organs are ________ derived but maturation occurs in _______________

For B cells = ____________

For T cells = _________

Answer 27

Primary lymphoid organs are Bone Marrow derived but maturation occurs in Lymphoid Organs

For B cells = Bone marrow

For T cells = Thymus

Question 28

What do we mean by maturation for Lymphocytes?

Answer 28

Where they learn to differentiate between self and non-self.

Question 29

What is the difference between Primary and Secondary Lymphoid organs?

Answer 29

Primary lymphatic organs are where lymphocytes are formed and mature. They provide an environment for stem cells to divide and mature into B- and T- cells:

• There are two primary lymphatic organs: the r_ed bone marrow_ and the t_hymus gland._
• B_oth T-cell and B-cells are ‘born’ in the bone marrow._
• However, whereas B cells also mature in the bone marrow, _T-cells have to migrate to the thymu_s, which is where they mature in the thymus.

Secondary lymphoid tissues are arranged as a series of filters monitoring the contents of the extracellular fluids, i.e. lymph, tissue fluid and blood.

• The lymphoid tissue filtering each of these fluids is arranged in different ways. Secondary lymphoid tissues are also w_here lymphocytes are activated._
• These include: lymph nodes, tonsils, spleen, Peyer’s patches and mucosa associated lymphoid tissue (MALT).

Question 30

What are the functions of Primary and Secondary Lymphoid organs (in 2 sentence)

Answer 30

Primary: where lymphocytes are formed and mature

Secondary: generation of a_daptive immune response_

Question 31

Clinical relevance- describe lymph node enlargement

Answer 31

Lymph Node Enlargement

• Reactive such as viral infection, local bacterial infection
• Malignant such as of lymphoid tissue (lymphoma) or metastatic spread

Question 32

Clinical relevance- describe Lymphocytosis

Answer 32

Lymphocytosis- Increase in Lymphocytes

• Reactive such as viral infections (e.g. infectious mononucleosis (EBV infection))
• Malignant such as chronic lymphocytic leukaemia

Question 33

Clinical relevane- describe lymphopenia

Answer 33

Lymphopenia

Lymphopenia is seen in:

• HIV infection with CD4 positive T helper cells (profound T cell deficit)
• Others such as congenital immune defects, steroid therapy, severe bone marrow failure

It may be associated with increased risk of opportunistic infection, malignancies.