Page 108 - Concise Pathology for Exam Preparation ( PDFDrive )

5 Diseases of Immunity 93

• �Macrophages are important effector cells in delayed hypersensitivity and humoral
immunity.

NK (Natural Killer) Cells
• �Constitute10–15% of circulating lymphocytes
• �Lack TCR or BCR
• �Also called large granular lymphocytes (larger than small lymphocytes and have abun-
dant azurophilic granules)
• �Express CD2, CD16 (Fc receptor for IgG) and CD56

• �CD 16 aids in type II hypersensitivity (antibody-dependent cell-mediated cytotoxic-

o
ity ADCC) by conferring on NK cells the ability to kill infected cells and tumour

r

cells without prior exposure or activation by them. The function CD 56 not

o
f
s
i

clear.
• �NK cell activity is regulated by stimulatory (NKG2D) and inhibitory (killer cell
immunoglobulin-like receptors and CD94 family of lectin receptors) influences.
• �Secrete TNF-a, IFN-g and GMCSF that help NK cells communicate with other cells of

immune system.
Innate Lymphoid Cells (ILCs)
population of lymphocytes that lack TCRs but generate cytokines similar to
• � A

T lymphocytes (different subsets produce IFN-g, IL-5, IL-17, IL-22)

• �Their functions include
• �Early defence against infections
• �Elimination of stressed cells
• �Influencing differentiation of T lymphocytes
Q. Enumerate the differences between T lymphocytes and
B lymphocytes.
Ans. Differences between T and B lymphocytes are shown in Table 5.1.
TABLE 5.1. Differences between T lymphocytes and B lymphocytes
Features T cell � B cell
Origin Stem cells in bone marrow n thymus Stem cells in bone marrow n secondary
lymphoid organs
Life span • Blasts: several days • Blasts: several days
• Small T cells: months to years • Small B cells: ,1 month
Location

(i) Lymph node Para/deep cortex Germinal centre, superficial cortex

(ii) Spleen Periarteriolar sheath Germinal centre, red pulp

(iii) Peyer’s patches Perifollicular zone Follicular centre
Percentage population in

(i) Blood 80% 20%
(ii) Bone marrow Rare Numerous

(iii) Lymph node 85% 15%

Surface markers

(i) TCR Ag receptor Present Absent

(ii) Surface lg Absent Present

(iii) Fc receptor Absent Present

(iv) Complement receptor Absent Present
(v) CD markers • T (helper): CD4,3,7,2 CD19,21,23

• T (suppressor): CD8,3,7,2

Functions (i) CMI via cytotoxic T cells (i) Precursors of plasma cells

(ii) Delayed hypersensitivity via CD41 (ii) Contribute to humoral immunity by
T cells synthesizing specific antibodies (Igs)
mebooksfree.com