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Figure 14.7 Common variations in neutrophil morphology.

as in megaloblastic anaemia, uraemia, and sometimes in T lymphocytes i.e. thymus-dependent lymphocytes, which CHAPTER 14
leukaemia. mature in the thymus and are also known as thymocytes.
iv) Pelger-Huët anomaly is an uncommon autosomal They are mainly involved in direct action on antigens and
dominant inherited disorder in which nuclei in majority of are therefore involved in cell-mediated immune (CMI) reaction
neutrophils are distinctively bilobed (spectacle-shaped) and by its subsets such as cytotoxic (killer) T cells (CD3+), CD8+
coarsely staining chromatin. Acquired pseudo-Pelger-Huët T cells, and delayed hypersensitivity reaction by CD4+ T cells.
abnormality may occur in acute infections or in MDS. B lymphocytes i.e. bone marrow-dependent or bursa-
However, the physiologic role of multilobed nucleus of equivalent lymphocytes as well as their derivatives, plasma
neutrophils is unknown and the bilobed anomaly is an cells, are the source of specific immunoglobulin antibodies.
innocuous condition. They are, therefore, involved in humoral immunity (HI) or
circulating immune reactions.
DEFECTIVE FUNCTIONS. The following abnormalities in
neutrophil function may sometimes be found: NK cells i.e. natural killer cells are those lymphocytes which
morphologically have appearance of lymphocytes but do not
1. Defective chemotaxis e.g. in a rare congenital abnor- possess functional features of T or B cells. As the name
mality called lazy-leucocyte syndrome; following cortico- indicates they are identified with ‘natural’ or innate immunity
steroid therapy, aspirin ingestion, alcoholism, and in myeloid and bring about direct ‘killing’ of microorganisms
leukaemia. (particularly certain viruses) or lysis of foreign body.
2. Defective phagocytosis due to lack of opsonisation e.g. Disorders of Leucocytes and Lymphoreticular Tissues
in hypogammaglobulinaemia, hypocomplementaemia, after PATHOLOGIC VARIATIONS. A rise in the absolute count
splenectomy, in sickle cell disease. of lymphocytes exceeding the upper limit of normal (above
3. Defective killing e.g. in chronic granulomatous disease, 4,000/μm) is termed lymphocytosis, while absolute lympho-
Chédiak-Higashi syndrome, myeloid leukaemias. cyte count below 1,500/μm is referred to as lymphopenia.
Lymphocytosis. Some of the common causes of lympho-
cytosis are as under:
Lymphocytes
1. Certain acute infections e.g. pertussis, infectious
MORPHOLOGY. Majority of lymphocytes in the peripheral mononucleosis, viral hepatitis, infectious lymphocytosis.
blood are small (9-12 μm in diameter) but large lymphocytes 2. Certain chronic infections e.g. brucellosis, tuberculosis,
(12-16 μm in diameter) are also found. Both small and large secondary syphilis.
lymphocytes have round or slightly indented nucleus with 3. Haematopoietic disorders e.g. lymphocytic leukaemias,
coarsely-clumped chromatin and scanty basophilic lymphoma, heavy chain disease.
cytoplasm. Plasma cells are derived from B lymphocytes 4. Relative lymphocytosis is found in viral exanthemas,
under the influence of appropriate stimuli. The nucleus of convalescence from acute infections, thyrotoxicosis,
plasma cell is eccentric and has cart-wheel pattern of clumped conditions causing neutropenia.
nuclear chromatin. The cytoplasm is characteristically deeply Lymphopenia. Lymphopenia is uncommon and occurs in
basophilic with a pale perinuclear zone. Plasma cells are the following conditions:
normally not present in peripheral blood but their patho- 1. Most acute infections.
logical proliferation occurs in myelomatosis. Reactive 2. Severe bone marrow failure.
lymphocytes (or Turk cells or plasmacytoid lymphocytes) 3. Corticosteroid and immunosuppressive therapy.
are seen in certain viral infections and have sufficiently 4. Widespread irradiation.
basophilic cytoplasm that they resemble plasma cells.
As discussed in Chapter 4, functionally, there are 3 types
of lymphocytes and possess distinct surface markers called Monocytes
clusters of differentiation (CD) which aid in identification of MORPHOLOGY. The monocyte is the largest mature
stage of their differentiation: leucocyte in the peripheral blood measuring 12-20 μm in