PARASITOLOGY

PARASITOLOGY

The sinusoids (spaces) are penetrated by arterioles and venules with the capsular

membrane penetrating into the reticulum forming trabeculae. There are two distinct regions

within the inner zones: the white pulp and the red pulp.

n White pulp is composed mainly of lymphocytes located around arterioles. Immedi-

ately surrounding the arteriole is a sheath of T cells known as the periarteriolar sheath

(PAS). On the periphery of the PAS are clusters of B cells alongside a germinal cen-

tre which produces more lymphocytes. About 50% of the total lymphocytes within

the spleen are B cells and 30–40% are T cells.

n Red pulp is composed of a mainly of red blood cells with lymphocytes macrophages

and giant cells.

5.5.1. 3The lymph nodes

The lymph nodes are small (about 1 cm diameter) ovoid bodies scattered throughout the

body. Each one is supplied with efferent and afferent lymphatic ducts, arteries and veins.

An outer capsule encloses a cellular reticulum, interspersed with dendritic lymphocytes

and ordinary macrophages.

Bone marrow

T cell precursor

Thymus

Mature T cell

T helper cell

CD4+

T cytotoxic

CD8+

T suppresor

cell

T DTH

cell

T dependent areas of lymph nodes and spleen

• Figure 5.7A precursor
  T cell migrates to the
  thymus where it is
  processed into a mature
  T cell. Within the T cell
  zones of lymph nodes and
  the spleen the mature
  T cell differentiates into
  at least four different
  phenotypes. The T cells
  have T cell antigen
  receptors and MHC class I
  molecules on their surface
  membranes and T helper
  cells have MHC class II.