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I have a few questions in regards to attraction/stimulation in the immune system.

  1. What attracts leukocytes and antibodies to pathogens in the first place?
  2. What attracts CD4+ cells to professional antigen-presenting cells (APC)?
  3. What attracts CD8+ cells to cells with an antigen on a MHC-1 protein?
  4. What attracts macrophages to pathogens that have been tagged with antibodies?

Is it just a case of everything bumping into each other and if cells (and antibodies??) bump into chemokines and/or cytokines they will be stimulated (and not attracted) to stay around that area moving to an area of a greater concentration of chemokines and/or cytokines?

That said point 1 can occur without chemokines and/or cytokines (in the case of antibodies, they could be taken/administered by the person). While in case of point 3, (I may be wrong here) but chemokines and/or cytokines may not be present in the case of MHC-1?

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What attracts leukocytes and antibodies to pathogens in the first place?

They just bump into them. If secreted antibody is already present in the blood then complement system can be activated.

What attracts CD4+ cells to professional antigen-presenting cells (APC)?

APC release chemokines. All that is known is that this is a CC-type chemokine and signals via CCR4/CCR8 receptors. See this list of articles (from Google Scholar). This study reports a peptide called Chemrin that promotes chemotaxis via ChemR23 receptor.

What attracts CD8+ cells to cells with an antigen on a MHC-1 protein?

CD8+/NK cells are activated by CD4+ cells before they kill their target. The MHC-1+antigenic peptide is just a mark for the cells that are to be attacked, as far as I understand.

What attracts macrophages to pathogens that have been tagged with antibodies?

Complement factors.

NOTE: Many of these concepts are old but still relevant. You should check out recent articles in this area for novel/atypical mechanisms.

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Regarding the answer to the first question: yes, if we are talking about circulating pathogens. But if the pathogen has cytotoxic effects on a tissue, the release of damaged cell components may attract immune system cells by chemotaxis. –  Cornelius Jul 22 at 10:23
    
yeah forgot to add that.. Cells can release type-1 interferons. –  WYSIWYG Jul 22 at 10:26
    
Brilliant, thank-you! I've been reading up on the self non-self theory & the danger theory..So was trying to arduously identify some of the danger signals that were already present. And thank-you @Cornelius –  Soap Jul 22 at 11:05

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