Changes

<p>[[High Endothelial Venules|High endothelial venules (HEV)]] facilitate lymphocyte access to the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] from the bloodstream. Once inside the lymph node, the naive lymphocytes search for antigens. If there are no antigens present, the naive lymphocytes leave via the efferent lymphatic vessel and return back to the bloodstream. Each lymphocyte can search several [[:Category:Secondary Lymphoid Tissue|secondary lymphoid organs]] each day. This process is called '''surveillance'''.</P>

<p>[[High Endothelial Venules|High endothelial venules (HEV)]] facilitate lymphocyte access to the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] from the bloodstream. Once inside the lymph node, the naive lymphocytes search for antigens. If there are no antigens present, the naive lymphocytes leave via the efferent lymphatic vessel and return back to the bloodstream. Each lymphocyte can search several [[:Category:Secondary Lymphoid Tissue|secondary lymphoid organs]] each day. This process is called '''surveillance'''.</P>

<p>If a naive lymphocyte recognises an antigen then it differentiates into its adult (mature) form. [[T cell differentiation#Dendritic Cells|Interdigitating dendritic cells]] present antigen to T cells and [[B cell differentiation#Follicular Dendritic Cells|follicular dendritic cells]] present antigen to B cells.</p>

<p>If a naive lymphocyte recognises an antigen then it differentiates into its adult (mature) form. [[T cell differentiation#Dendritic Cells|Interdigitating dendritic cells]] present antigen to T cells and [[B cell differentiation#Follicular Dendritic Cells|follicular dendritic cells]] present antigen to B cells.</p>

<p>B cells proliferate into [[B cell differentiation#Plasma cells|plasma cells]] in germinal centres, producing antibody.</p>

<p>B cells proliferate into [[B cell differentiation#Plasma cells|plasma cells]] within sectors of the lymph nodes known as germinal centres, producing antibody.</p>

<p>T cells leave the lymph node in '''attack mode''' to locate the infectious organism. The surface molecule L-selectin (which allows the naive lymphocyte to enter the lymph node via an [[Lymph Nodes - Anatomy & Physiology#High endothelial venules|HEV]]) is replaced by the adhesion molecule VLA-4. At the site of inflammation, the VLA-4 receptor recognises VCAM-1 on endothelial cells and the [[Lymphocytes#T cell|T cell]] enters the site of disease. [[Lymphocytes#Helper CD4+|CD4+ T cells]] search for infected macrophages and [[Lymphocytes#Cytotoxic CD8+|CD8+ T cells]] look for virus infected cells creating an immune response. After the infection has been defeated, memory cells develop which express L-selectin (rather than VLA-4) and continue to search the body in surveillance mode in case the host is re-infected with the disease producing organism.

<p>T cells leave the lymph node in '''attack mode''' to locate the infectious organism. The surface molecule L-selectin (which allows the naive lymphocyte to enter the lymph node via an [[Lymph Nodes - Anatomy & Physiology#High endothelial venules|HEV]]) is replaced by the adhesion molecule VLA-4. At the site of inflammation, the VLA-4 receptor recognises VCAM-1 on endothelial cells and the [[Lymphocytes#T cell|T cell]] enters the site of disease. [[Lymphocytes#Helper CD4+|CD4+ T cells]] search for infected macrophages and [[Lymphocytes#Cytotoxic CD8+|CD8+ T cells]] look for virus infected cells creating an immune response. After the infection has been defeated, memory cells develop which express L-selectin (rather than VLA-4) and continue to search the body in surveillance mode in case the host is re-infected with the disease producing organism.