Our immune system can be broadly categorized into a fast-responding system and a slow-responding system:
1. Innate or natural system (fast)
Fast acting system (0-96 hours) which serves as the first-line of defense
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Recongnizes invading substance (antigens) which can be pathogens such as bacteria, viruses, fungi, and parasites, or smaller proteins fragments that the pathogens express
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Releases chemical cues (cytokines) to alarm and activate the Adaptive response
2. Adaptive system (slow)
Activated by the alarm bell sounded by the Innate system
It mounts a response by producing B-cells and T-cells, which is a slow process (can take anywhere from >96 hours to a few days/week)
2.1 B-cells
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Recognize the antigens and produce antibodies to fend off the infection
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Once infection is cleared, the production of antibodies is slowed down and the B-cells convert from antibody-producing plasma B-cells to memory B-cells that persist in our body for years
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When a future infection is detected, they quickly convert to plasma B-cells and mount a faster and stronger immune response
2.2 T-cells
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There are two kinds of T-cells: helper T-cells and killer T-cells
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Helper T-cells release more cytokines (ie sounds the alarm bells) to prime the maturation of B-cells
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Killer T-cells directly kill the infected or hijacked cells
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Remain in the body as memory T-cells once infection is cleared. These memory lymphocytes remain dormant until same pathogen or protein fragments are encountered again
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The following is from this news article How kids’ immune systems can evade COVID published on Dec 10, 2020
A growing body of evidence suggests why young children account for only a small percentage of COVID-19 infections: their immune systems seem better equipped to eliminate SARS-CoV-2 than are adults’.
Some children who do get infected never test positive for the virus on a standard RNA test, even if they develop symptoms and have antibodies specific to SARS-CoV-2. Their immune system sees the virus “and it just mounts this really quick and effective immune response that shuts it down, before it has a chance to replicate to the point that it comes up positive on the swab diagnostic test”, says immunologist Melanie Neeland. The source of children’s immune advantage is thought to arise from one — or several — of these factors:
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Children’s T cells are untrained, so they might have a greater capacity to respond to new viruses
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Children might have a strong innate immune response from birth, although that raises the question of why it isn’t seen with other viruses that can cause severe disease in children
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It could be thanks to the protection of antibodies to seasonal common-cold coronaviruses, which run rampant in children
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Kids might receive a smaller dose when exposed to SARS-CoV-2, because their noses contain fewer of the ACE2 receptors that the virus uses to gain access
The following pics are from this article published on Feb 9, 2021
