Neutrophils that enter inflammatory sites can survive for days, but macrophages are very short lived and only survive for hours

The numbers of circulating neutrophils and macrophages greatly expand in numbers in response to an infection

Both neutrophils and macrophages contain abundant acidic cytoplasmic granules that can destroy ingested microbes or released to kill microbes too large to be ingested

Macrophages that enter inflammatory sites can survive for days, but neutrophils are very short lived and only survive for hours

1: Basophil, 2: Lymphocyte, 3: Basophil, 4: Neutrophil

1: Neutrophil, 2: Lymphocyte, 3: Eosinophil, 4: Basophil

1: Eosinophil, 2: Lymphocyte, 3: Neutrophil, 4: Macrophage

1: Neutrophil, 2: Macrophage, 3: Lymphocyte, 4: Basophil

Bone marrow

Thymus

Lymph node

Spleen

Lck binds to CD4 and leads to phosphorylation of ITAM

Lck binds to CD3 to induce direct signalling through the TCR

Lck binds to the ITAMs and leads to phosphorylation

Lck binds to the TCR cytoplasmic tail and CD4 to link and increase the avidity between the APC and T cell

Lck binds to CD4 and leads to phosphorylation of ITAM

Lck binds to CD3 to induce direct signalling through the TCR

Lck binds to the ITAMs and leads to phosphorylation

Lck binds to the TCR cytoplasmic tail and CD4 to link and increase the avidity between the APC and T cell

The pairing and binding of phosphorylation sites on partner proteins, to initiate and enhance activation

Molecular degradation of the phosphorylated protein to stop signalling

The generation of binding sites for other molecules

The immediate transportation of phosphorylated proteins to the nucleus, activating transcription factors

CD4 and CD8 both have a role in T cell activation

CD4 and CD8 determine with which MHC class the T cell will interact

CD4 and CD8 expression is upregulated on activated T cells once the TCR has engaged with peptide:MHC

Both CD4 and CD8 bind to MHC domains that are distinct from the peptide binding cleft

The source of antigen to maintain proliferation is reduced or absent

Innate cells (especially neutrophils) recruited to the site of infection by helper T cells, will kill these cells after responding to the pathogen

B cells out-compete T cells in the lymph node so that sufficient antibody concetrations can be generated

T cells generated through clonal expansion have a short (~7-10 day) lifespan

TNF-α and IL-2

TGF-β and IL-10

IFN-γ and IL-12

 IL-4 and IL-5

The T cell produces an IL-2 receptor with much stronger affinity

IL-2 binds the IL-2 receptor on neighbouring T cells promoting their differentiation into T helper cells

IL-2 binds the IL-2 receptor on the antigen expressing dendritic cell to enhance the presentation of peptide

IL-2 promotes the migration of the T cell towards the germinal centre