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Chapter 9 White cells: Lymphocytes / 137

Germinal follicle Follicular dendritic cells
Mantle zone
Marginal zone

Plasma cells
Bone
marrow
Memory B cells
Naive Apoptosis
B cells

B cell proliferation IgG class switching and
and somatic hypermutation generation of memory
B cell or plasma cell
Positive selection of B cells
by binding to follicular
dendritic cells or apoptosis
of B cells

Figure 9.10 Generation of a germinal centre. B cells activated by antigen migrate from the T zone to the follicle

where they undergo massive proliferation. Cells enter the dark zone as centroblasts and accumulate mutations
in their immunoglobulin V genes. Cells then pass back into the light zone (Fig. 9.9 ) as centrocytes. Only those
cells that can interact with antigen on follicular dendritic cells and receive signals from antigen - specifi c T cells
(Fig. 9.8 ) are selected and migrate out as plasma cells and memory cells. Cells not selected die by apoptosis.

orbital oedema) are not uncommon. The rash may

Table 9.3 Causes of lymphocytosis.
follow therapy with amoxicillin or ampicillin.
5 Palpable splenomegaly occurs in over half of
Infections
patients and hepatomegaly in approximately 15%.
Acute: infectious mononucleosis, rubella,
pertussis, mumps, acute infectious Approximately 5% of patients are jaundiced.
lymphocytosis, infectious hepatitis, 6 Peripheral neuropathy, severe anaemia (caused
cytomegalovirus, HIV, herpes simplex or by autoimmune haemolysis) or purpura
zoster (caused by thrombocytopenia) are less frequent
Chronic: tuberculosis, toxoplasmosis, complications.
brucellosis, syphilis

Chronic lymphoid leukaemias (see Chapter 17 ) Diagnosis

Acute lymphoblastic leukaemia
Pleomorphic a typical l ymphocytosis
Non - Hodgkin lymphoma (some) A moderate rise in white cell count (e.g. 10 –
9
20 × 10 /L) with an absolute lymphocytosis is usual,
Thyrotoxicosis
and some patients have even higher counts. Large
numbers of atypical lymphocytes are seen in the
HIV, human immunodefi ciency virus.

peripheral blood film (Fig. 9.11 ). These T cells are