HSC Biology Syllabus Notes

Module 7 / Inquiry Question 3

Inquiry question: How does the human immune system respond to exposure to a pathogen?

Learning Objective #1 – Investigate and model the innate and adaptive immune systems in the human body 

Learning Objective #2 – Explain how the immune system responds after primary exposure to a pathogen, including innate and acquired immunity

Week 11 Homework Questions

Week 11 Curveball Questions

Week 11 Extension Questions

Solutions to Week 11 Questions 


Learning Objective #1 - Investigate and model the innate and adaptive immune system in the human body

Let’s first talk about adaptive immunity.

We have already talked about how Helper T cells can activate B-cells in previous week’s notes. This process of B-cells being activated by Helper T cells to produce antibodies is called the Humoral response which is a type of adaptive immunity. This is also known as antibody-mediated immunity.

If you are not sure, please re-visit last week’s notes under third line of defence.

This is adaptive immune response (adaptive immunity) is useful to eliminate:

  • Toxins produced by bacteria.

  • Bacteria and viruses outside cells.

Vice versa, cell-mediated immunity is process whereby activated Helper T cells clone and differentiates into other types of Helper T cells, each capable of activating other T cells (e.g. cytotoxic T cells via cytokines). This adaptive immunity is useful against:

  • Bacteria and viruses inside cells.

  • Protozoa, fungi, flatworms and roundworms.

  • Cancerous cells and transplanted foreign tissues.

Now, let’s visit innate immune system. Unlike adaptive immune response, this is NOT specific to a certain pathogen!

Therefore, the innate immune system are the first and second line of defence.

Phagocytosis was already explored in last week’s notes. 

However, just for fun, we will go into a bit more detail here this week.

Phagocytes could be macrophages, neutrophils and dendritic cells.

Macrophages and dendritic cells has pattern recognition receptors (PRR) which allow them to recognise pathogen associated molecular patterns (PAMPs) on microbes. PAMPs is sometimes referred to microbes associated molecular patterns (MAMPs) which we referred to as in the last week’s notes when we looked at plant’s general-induced immunity. 

These pattern recognitions receptors are specified by genes which are inherited from parents and thus are subjected and product of evolution.

Once the macrophage or dendritic cell recognises the PAMPs or MAMPs using its pattern recognition receptors, they are able to engulf the pathogen or antigen. The macrophage or dendritic cell with the engulfed antigen will travel to the lymph whereby it is trapped by the lymph nodes. It is a the lymph nodes where the macrophages or dendritic cell with engulfed antigen will activate Helper T cell directly (or inactivate via B cell). Therefore, here innate immunity will stimulate the adaptive immune response.

Recap! Here is a flowchart from Inquiry Question 2's Notes on Adaptive Immunity

Adaptive-Immunity-Flowchart-Editedx (1).png


Learning Objective #2 - Explain how the immune system responds after primary exposure to a pathogen, including innate and acquired immunity.

Innate immunity was already talked about in last week’s notes under ‘First Line of Defence’ and ‘Second Line of Defence’. 

Acquired Immunity here can take in two forms it can be actively acquired or passively acquired. 

Since actively acquired immunity involves the production of memory T cells and memory B cells, such immunity to the pathogen will last longer than passively acquired immunity. 

This is because passively acquired immunity involves the uptake of antibodies which only lives for several weeks or 4 months at max in the blood. Comparatively, T and B memory cells can remain in circulation in the blood and lymph for many years!

In next week’s notes, we will looking into both actively acquired and passively acquired immunity. So, we will not be exploring it here this week. 

Also, in next week’s notes, we will also be exploring how the immune system responds after secondary exposure to a pathogen! This is when memory B cells and memory T cells become useful!