Teaching Matters

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Teaching Matters 2018 | Presentation Details | 2018


The Virtual Lymph Node: using the 'Birthday Paradox' to explain lymphocyte cooperation in adaptive immunity


Bruce Lyons, School of Medicine


Excellent teaching happens by design

Presentation Type



Flexible Learning Space 2




The interactive Virtual Lymph Node Game was developed to explain key concepts in immunology to undergraduate students. Each lymphocyte has a single specificity of receptor able to recognise pathogens, but they are randomly generated in enormous numbers. This provides a very good way to combat almost any disease-causing microorganism. However, a B lymphocyte recognising a pathogen also has to find a helper T cell recognising the same foreign material (or antigen) in order to become activated and make antibody.

The Virtual Lymph Node Game is based on the ‘birthday paradox’; when 50 or more people are randomly selected, there is a 97% or greater probability of 2 or more of them sharing a birthday (day and month) (Gardner, 1957).

I divide the lecture theatre into two; one part being the T cell area, and the other the B cell area, using it as a model to explain how lymph fluid enters, carrying antigen presenting cells and free antigen, which interact with T and B lymphocytes (students!), with the specificity determined by birth date. We can then see if B and T cells in our virtual lymph node share this date. The outcome could be only a B cell (fails to get T cell help), only a T cell (helpful in activating other cells) or neither T or B cells (host organism is dead!). The different outcomes also help explain aspects of immunity. You can also ‘cheat’ if you know that one of the students shares a birthday with you; students seems to like the idea of lecturer as pathogen!


Gardner, M. (1957). Paradoxes dealing with birthdays, playing cards, coins, crows and red-haired typists. Scientific American, 196 (4) April 1957

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