PARASITOLOGY

INTRODUCTION TO HOST RESPONSE

APC. In addition and occurring simultaneously, a whole range of wandering phagocytic

cells and natural killer (NK) cells become primed. Circulating soluble compounds such

as complement, cytokines and soluble antibodies are now released into the system.

n 5.5 AN OUTLINE OF THE ADAPTIVE IMMUNE SYSTEM

The organs that are involved in the immune response are bone marrow, thymus, spleen

and the numerous lymph nodes scattered round the body, including those associated

with the gut, lungs etc. Bone marrow and the thymus are the primary lymphoid organs

and the others are secondary lymphoid organs.

Nucleus

Macrophage

Pathogen
PAMPs
PRR

Peptide

fragments

of pathogen

(antigen)

Costimulatory molecule

CD4

MHC class II molecule

Antigen

T cell antigen receptor

CD3

Activated T helper

cell

Antigen-presenting

cell in lymph node

or spleen

• Figure 5.3The Pathogen
  Receptor Region (PRR) on
  phagocytic surveillance
  cells such as macrophages
  identifies the Pathogen
  Associate Molecular
  Pattern (PAMP) on the
  pathogen. The phagocytic
  cell engulfs the pathogen.
  Once inside the cell it is
  digested and peptide
  fragments of the pathogen
  are released.


• Figure 5.4Within a
  phagocyte the digested
  peptide fragments of the
  pathogen are transported
  to the cell surface where
  they become associated
  with the Major
  Histocompatibility Complex
  (MHC) class II molecules.
  The costimulatory
  molecules on the
  phagocyte are activated.
  The phagocytic cell now
  referred to as Antigen
  Presenting Cell (APC) and
  migrates to a lymph node
  or spleen where it
  presents the antigen
  peptide to a T helper cell.