Changes

** Cytotoxic T lymphocytes (CTLs) kill healthy cells mistakenly thinking they are infected by a virus.

** Cytotoxic T lymphocytes (CTLs) kill healthy cells mistakenly thinking they are infected by a virus.

Exposure to antigen causes [[Lymphocytes - WikiBlood#Helper CD4+|'''CD4+ T helper cells''']] to be activated leading to colonal expansion (takes 1-2 weeks). On subsequent exposure with the same antigen sensitised [[Lymphocytes - WikiBlood#Helper CD4+|'''CD4+ T helper cells''']] secrete cytokines which attract and activate macrophages. The macrophages have an increased ability to phagocytose pathogens, which is very important for the clearance of intracellular pathogens. However if antigen exposure persists, the lytic products of the macrophages can damage healthy tissues.

Exposure to antigen causes [[Lymphocytes - WikiBlood#Helper CD4+|'''CD4+ T helper cells''']] to be activated leading to colonal expansion (takes 1-2 weeks). On subsequent exposure with the same antigen sensitised [[Lymphocytes - WikiBlood#Helper CD4+|'''CD4+ T helper cells''']] secrete [[Cytokines - WikiBlood|cytokines]] which attract and activate macrophages. The [[Macrophages - WikiBlood|macrophages]] have an increased ability to phagocytose pathogens, which is very important for the clearance of intracellular pathogens. However if antigen exposure persists, the lytic products of the macrophages can damage healthy tissues.

==2 types:==

==2 types:==

|-  

|-  

| '''Pathogenesis'''

| '''Pathogenesis'''

| Type I

| [[Type I Hypersensitivity - WikiBlood|Type I]]

| Type IV

| [[Type IV Hypersensitivity - WikiBlood|Type IV]]

|-

|-

| '''Time'''

| '''Time'''

|-

|-

|'''Pathology'''

|'''Pathology'''

| mast cells, eosinophils

| [[Mast cells - Wikiblood|mast cells]], [[Eosinphils - Wikiblood|eosinophils]]

| mononuclear cells

| mononuclear cells

|}

|}