Travel to Health

Our immune system plays a crucial role in protecting our body against pathogens, but sometimes there is an exaggerated response. This exaggerated response is triggered by the interaction of the immune system with an antigen (allergen) and is referred to as hypersensitivity . Hypersensitivity is believed to be the cause of  allergy  and some  auto-immune disease . In this article, we will discuss mainly Type IV Hypersensitivity . Classification Immunoreactants Clinical Presentation Type I Mast cell mediated, IgE dependent (anaphylactic, and IgE independent) Anaphylaxis, urticaria, angioedema,  sthma , and  hay fever Type IIa Antibody-mediated cytotoxic reactions (IgG and IgM antibodies complement often involved) Immune cytopenias Type IIb Antibody-mediated cell-stimulating reactions Graves disease and chronic idiopathic urticaria Type III Immune complex–mediated reactions complement involved Serum sickness and vasculitis Type IVa Th1...

It is clear from this [4]  and other studies that the immune response in hospitalized patients with severe COVID-19 is  characterized by  lymphopenia  and the expression of molecules associated with ongoing inflammation , [5]  whereas these same molecules are expressed at a lower level in people with mild or moderate disease. Figure 1.   Immune responses to COVID-19 infection (source: [4]) a) Higher IFN-α in in people with severe disease (cf. moderate disease) b) Higher expression of IFN-λ only in people with severe disease c) Level of TNF-α (a inflammation-promoting cytokine) correlated with viral load in the nasal passages d) Viral load declined over time in people with moderate disease (cf. severe disease) e) IL-5 upregulated as people developed severe disease (cf. moderate disease) f) Levels of CD4 and CD8 T cells were lower in people with moderate or severe disease (cf. healthy controls) Immune Responses to COVID-19 Infection A dysregulated immune...

  Line of Defense Timeline Cells Antigen Dependency Examples Innate (non-specific) First Immediate response (0 -96 hours) Natural killer cells, macrophages, neutrophils, dendritic cells, mast cells, basophils, eosinophils Independent Skin, hair, cough, mucous membranes, phagocytes, granulocytes Adaptive (specific) Second Long term (>96 hours) T and B lymphocytes Dependent Pus, swelling, redness, pain, T and B lymphocyte response Table 1.  Innate immune response vs adaptive immune response (source: [3]) Figure 1.  DCs—Messengers between Innate and Adaptive Immune Systems Dendritic cells (DCs) represent a heterogeneous family of immune cells that link innate and adaptive immunity . The main function of these innate cells is to capture, process, and present antigens to adaptive immune cells and mediate their polarization into effector cells . Figure 2.   COVID-19 vaccines immune activation modes (Source: [8]) Dendrite Cells Dendritic cells  (DC) are...