71.  The process of eliminating those lymphocytes that react or respond against self-antigens is called  
A.  phagocytosis.
B.  inflammation.
C.  negative selection.
D.  activation of complement.
E.  natural selection.

72.  Positive selection of lymphocytes refers to the  
A.  processing of an antigen by a macrophage.
B.  proliferation of natural killer cells.
C.  production of antigen-specific antibodies.
D.  survival of pre-B and pre-T cells that are capable of an immune response.
E.  replication of memory cells.

73.  Primary lymphatic organs include the  
A.  tonsils and spleen.
B.  thymus and lymph nodes.
C.  red bone marrow and thymus.
D.  red bone marrow and lymph nodes.

74.  Which of the following is NOT a secondary lymphatic organ?  
A.  spleen
B.  lymph node
C.  lymphatic nodule
D.  thymus gland

75.  What areas of an antigen are recognized by lymphocytes so that they can respond?  
A.  major histocompatibility complexes
B.  antigenic determinants
C.  T-cell receptors
D.  epitopes
E.  Both antigenic determinants and epitopes are correct.

76.  The MHC (major histocompatibility complex) class molecules  
A.  are only found on B cells.
B.  are found in the nucleus of cells.
C.  allow the immune system to respond to antigens inside cells.
D.  are lipoproteins on cell surfaces.
E.  do not attach to plasma membranes.

77.  Different T-cell receptors can respond to different antigens because of different  
A.  variable regions in the structure of the receptors.
B.  epitopes in the receptor’s structure.
C.  selection processes.
D.  complement binding sites in the receptors.
E.  antigenic determinants.

78.  Lymphocyte activation can occur in several ways. However, in all cases  
A.  lymphocytes must recognize an antigen.
B.  helper T cells are activated first and they then stimulate other cells.
C.  antigen-presenting cells process the antigen and present it to the lymphocytes.
D.  cytokines released by the antigen stimulate the lymphocyte response.
E.  antigens must be able to recognize the lymphocytes.

79.  The MHC class I antigen complex displays a foreign antigen on the cell surface. This prompts the immune system to destroy  
A.  B cell clones.
B.  extracellular antigens.
C.  the displaying cell.
D.  mature red blood cells.
E.  the virus inside the cell, but not the cell.

80.  MHC class II molecules are found on  
A.  neutrophils, monocytes, and macrophages.
B.  dendritic cells, B cells, and helper T cells.
C.  monocytes, helper T cells, and neutrophils.
D.  B cells, macrophages, and dendritic cells.
E.  B cells, C cells and D cells.