breed [ bacteria bacterium ] breed [ cells cell ] breed [ macrophages macrophage ] breed [ neutrophils neutrophil ] bacteria-own [ energy target-patch amt-consumed ] macrophages-own [ consumed radius speed capacity] neutrophils-own [ consumed radius speed capacity] patches-own [ glucose chemical cell-present tissue-damage immune-chemicals targeted death-chance] globals [ seconds-per-frame macrophage-sense-distance ; How far away macrophages can sense chemical bacteria-size ; Bacteria size macrophage-radius ; Macrophage size neutrophil-radius ; Neutrophil size macrophage-motility neutrophil-motility cell-radius ; Body cell size reinforcements-coming ; Flag to indicate macrophage reinforcements are coming reinforcement-timer ; Timer to implement reinforcement delay reinforcement-count ; Number of macrophages per reinforcement glucose-diffusion-rate ; Diffusion rate of glucose in patches global-scale ; Global scale in micometers bacteria-reproduce-cost bacteria-reproduce-spread neutrophil-delay ; Initial delay for neutrophil arrival at infection site max-glucose-concentration ; Glucose concentration in the blood max-neutrophil-time max-neutrophil-count recruitment-delay chemical-dissipation-rate max-immune-chemical ] to setup-globals set recruitment-delay 1440 set seconds-per-frame 10 ; each time step is 10 seconds set global-scale 0.28 ; micrometers per pixel set bacteria-size 1 * global-scale set macrophage-sense-distance 4 set macrophage-radius 10.6 * global-scale ; set neutrophil-radius 4.2 * global-scale ; set neutrophil-motility 0.45 * global-scale * seconds-per-frame ; speed of neutrophil movement set macrophage-motility 0.15 * global-scale * seconds-per-frame ; speed of macrophage movement set cell-radius 2 * global-scale set reinforcements-coming true set reinforcement-timer recruitment-delay set reinforcement-count 1 set glucose-diffusion-rate 0.4 set bacteria-reproduce-cost 1 set neutrophil-delay 60 set max-glucose-concentration 100 ; 100 mg/dL set max-neutrophil-time 14400 * seconds-per-frame ; 4 hours (in seconds) set chemical-dissipation-rate 6 set max-immune-chemical 3000 end to setup clear-all setup-globals create-bacteria initial-bacteria-count [ initialize-bacteria ] ;create-cells cell-count ;[ ; set shape "circle 2" ; set color red ; set size cell-radius * 1.3 ; setxy random-xcor random-ycor ;] ask patches [ set glucose 1 ;set cell-present false set tissue-damage 0 set immune-chemicals 0 ] ask patches [set-color] reset-ticks end ; ************************************************************************ TO GO **************************************************************************************** to go ; Stop if reached total # ticks or all the intruders are destroyed if (not any? turtles) or (not any? bacteria) [ stop ] ask patches [set targeted false] ; Diffuse glucose diffuse glucose glucose-diffusion-rate ; Diffuse chemical diffuse chemical 0.2 ; Diffuse immune chemicals diffuse immune-chemicals 0.2 check-reinforcements if ticks = max-neutrophil-time [set max-neutrophil-count (count neutrophils)] ; If bacteria are present, simulation continues. Initiate neutrophil response. ; We're assuming that neutrophils are not intially present at t=0 when wounding occurs and bacteria are introduced if (ticks = neutrophil-delay) [ create-neutrophils 1 [ initialize-neutrophil ] ifelse ticks < max-neutrophil-time [set neutrophil-delay floor (neutrophil-delay + neutrophil-delay * (1 / (count neutrophils)))] [set neutrophil-delay floor (neutrophil-delay + neutrophil-delay * ((count neutrophils) / max-neutrophil-count))] ] ; Bacteria consume energy and release chemicals, ; then decide whether to move or divide ask bacteria [ react-to-immune-chemicals consume-energy decide-action ] ; Neutrophils move toward bacteria, consume them, and then ; call for reinforcements if they detect enough intruders nearby ask neutrophils [ move-to-bacteria release-immune-chemicals ; this must be before phagocytosis phagocytose ;signal-reinforcements ] ;create-macrophages initial-macrophage-count ;[ initialize-macrophage ] ; Macrophages move toward bacteria, consume them, ; can release chemicals to kill bacteria, and then ; call for reinforcements if they detect enough intruders nearby ; (macrophages calling for reinforcements is currently not active) ask macrophages [ move-to-bacteria release-immune-chemicals ; this must be before phagocytosis phagocytose ;signal-reinforcements ] ; Each patch of the ECM receives more glucose from the blood ; possibly gets tissue damage, ; and then sets its color based on the patch-view option ask patches [ increase-glucose increase-tissue-damage set-color ] tick ifelse display-consumed [ ask macrophages [ set label consumed] ] [ ask macrophages [ set label ""] ] end ; *********************************************************************** BACTERIA FUNCTIONS ***************************************************************************************************** to initialize-bacteria set shape "bug" set color green set size bacteria-size set energy random-float bacteria-reproduce-cost setxy random-xcor random-ycor end ; chemicals released by immune cells can kill bacteria to react-to-immune-chemicals if (random-float 1) < death-chance ; arbitrary but the more chemicals, the more chance the number will be over the threshold [ die ] end ; Consume energy and leave behind chemical ; Cells in the body can recognize parts of bacteria and respond with inflammatory signals ; Normally non-immune cells would also respond by releasing signaling chemicals ; but for our model we skip straight to immune cells responding to consume-energy ; Consume energy from local glucose set amt-consumed avg-bacteria-consumption-rate * 0.9 + random-float (avg-bacteria-consumption-rate * 0.2) if glucose < amt-consumed [ set amt-consumed glucose ] set energy (energy + amt-consumed) set glucose (glucose - amt-consumed) ; Leave behind a chemical that macrophages & neutrophils can sense ask patches in-radius 4 [ set chemical chemical + 1 ] end to decide-action ; If the bacterium has enough energy to reproduce, it does that. Otherwise it moves. ifelse energy > bacteria-reproduce-cost [ reproduce ] [ move-to-glucose ] end ; cell division of bacteria to reproduce ; As long as the bacterium has enough energy, create a new bacterium ; Doubling time = 60min, so max is once per 1hr tick if energy > bacteria-reproduce-cost [ set energy (energy - bacteria-reproduce-cost) hatch 1 [ rt random-float 360 fd random 0.5] ] end ; bacteria want glucose (or other sugars/nutrients) as energy sources to move-to-glucose if(glucose < bacteria-reproduce-cost) [ ; Move to the closest patch with a sufficient amount of glucose set target-patch max-one-of (patches in-radius 2) [glucose] if target-patch != nobody [ face target-patch fd 1 + random-float 1 ] ] end ; *********************************************************************** IMMUNE CELL FUNCTIONS ********************************************************************************************* to initialize-neutrophil set radius neutrophil-radius set shape "circle 2" set color red set size neutrophil-radius * 2 set consumed 0 set speed neutrophil-motility set capacity 10 setxy random-xcor random-ycor end to initialize-macrophage set radius macrophage-radius set shape "circle 2" set color white set size macrophage-radius * 2 set consumed 0 set speed macrophage-motility set capacity 100 setxy random-xcor random-ycor end ; immune cells are attracted to infection so they can fight it to move-to-bacteria ; Move to the patch with the strongest chemical let sensed-patches (patches in-radius macrophage-sense-distance) with [not targeted] let potential-targets (sensed-patches with-max [chemical]) ; If more than half of our sensed patches have the same maximum chemical, ; Just pick a slightly deferred course and keep moving ifelse count potential-targets < (count sensed-patches) / 2 [ let target (one-of potential-targets) face target ask target [set targeted true] ] [ rt random 30 lt random 30 ] fd (speed * 0.8) + (random-float (speed * 0.2)) end ; some immune cells can fight bacteria by releasing chemicals that kill the bacteria ; Note for model implementation: releasing chemicals must be before phagocytosing otherwise it will never be activated ; because all bacteria within range will be gone to release-immune-chemicals let nearby-patches (patches in-radius (radius * 0.7)) if (count bacteria-on nearby-patches) > 10 [ ask nearby-patches [ set immune-chemicals min list max-immune-chemical (immune-chemicals + 1000) set death-chance ((immune-chemicals / max-immune-chemical) ^ 10 ) * immune-chemical-toxicity ] ] end ; some immune cells like neutrophils and macrophages can "eat" bacteria and destroy them to phagocytose let nearby-patches (patches in-radius radius) ask nearby-patches [set chemical 0] ; Eat the intruders and keep track of how many we've eaten if consumed < capacity [ set consumed consumed + (count bacteria-on nearby-patches) ask bacteria-on nearby-patches [ die ] ] set consumed max list 0 (consumed - phagocytosis-rate / 6) end ; should new immune cells be recruited? to signal-reinforcements ; Set the global reinforcement indicator which will be fulfilled ; after a delay let nearby-patches (patches in-radius (radius * 2)) if (count bacteria-on nearby-patches) > 1 [ set reinforcements-coming true ] end ; immune cells recruit other immune cells to help fight the infection to check-reinforcements if reinforcements-coming [ ; Count down the timer set reinforcement-timer reinforcement-timer - 1; ; If the timer is at zero, add the number of ; reinforcements and then reset the timer if reinforcement-timer <= 0 [ create-macrophages reinforcement-count [ initialize-macrophage ] set reinforcement-timer recruitment-delay ] ] end ; *********************************************************************** PATCH FUNCTIONS ********************************************************************************************* to set-color ; Choose to view the amount of chemical or if patch-view = "chemical" [ set pcolor scale-color cyan chemical 0 1000 ] if patch-view = "glucose" [ set pcolor scale-color blue glucose 0 3 ] if patch-view = "immune-chemicals" [ set pcolor scale-color red immune-chemicals 0 (max-immune-chemical) ] end ; replenish glucose and make chemicals from bacteria dissipate to increase-glucose ; Increase the ECM glucose levels if glucose <= 1 [ set glucose (glucose + (random-float max-glucose-replenishment-rate)) if chemical > 0 [set chemical max (list 0 (chemical - chemical-dissipation-rate))] ] end ; over time, the immune response to the bacteria can cause tissue damage to increase-tissue-damage ; increase tissue-damage if ((chemical ^ (0.02) + immune-chemicals ^ (0.2)) > 5) ; this calculation is arbitrary [set tissue-damage (tissue-damage + 10)] end @#$#@#$#@ GRAPHICS-WINDOW 543 15 1221 694 -1 -1 10.0 1 10 1 1 1 0 1 1 1 -33 33 -33 33 1 1 1 ticks 30.0 BUTTON 95 38 270 88 NIL setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 288 38 468 88 NIL go T 1 T OBSERVER NIL NIL NIL NIL 0 PLOT 15 299 541 692 Plot NIL NIL 0.0 10.0 0.0 10.0 true true "" "" PENS "bacteria" 1.0 0 -14439633 true "" "plot count bacteria" "total glucose" 1.0 0 -13345367 true "" ";plot sum [glucose] of patches" "macrophage recruitment" 1.0 0 -3026479 true "" "if reinforcement-timer = 1\n[\n plot-pen-up\n plotxy ticks 0 \n plot-pen-down\n plotxy ticks plot-y-max \n]" "total tissue damage" 1.0 0 -2674135 true "" "plot sum [tissue-damage] of patches / 10000" SLIDER 286 112 536 145 initial-bacteria-count initial-bacteria-count 1 5000 2490.0 1 1 NIL HORIZONTAL SLIDER 17 150 273 183 max-glucose-replenishment-rate max-glucose-replenishment-rate 0 0.1 0.04 0.01 1 NIL HORIZONTAL CHOOSER 15 242 162 287 patch-view patch-view "glucose" "chemical" "immune-chemicals" 2 MONITOR 366 189 533 238 Number of macrophages count macrophages 0 1 12 SWITCH 168 245 322 278 display-consumed display-consumed 1 1 -1000 MONITOR 332 244 536 289 Macrophage Recruitment Countdown reinforcement-timer 0 1 11 SLIDER 30 112 270 145 avg-bacteria-consumption-rate avg-bacteria-consumption-rate 0 0.005 0.0024 0.0001 1 NIL HORIZONTAL SLIDER 290 154 535 187 immune-chemical-toxicity immune-chemical-toxicity 0 1 0.1 0.01 1 NIL HORIZONTAL SLIDER 20 197 271 230 phagocytosis-rate phagocytosis-rate 0 1 0.12 0.01 1 NIL HORIZONTAL @#$#@#$#@ ## WHAT IS IT? In this project, cells of the innate (non-specific) immune system respond to a bacterial infection in a shallow, acute skin wound. The user can change rates in the model to compare the time for all the bacteria to be removed (bacterial clearance) in a healthy patient compared to a diabetic patient. Diabetic patients are at an increased risk of long-lasting bacterial infections because they have increased glucose sugar levels in their bloodstream and their immune cells are less effective at fighting infection. ## HOW IT WORKS Glucose is replenished from the blood stream at a constant rate. If bacteria have accumulated enough energy, they reproduce. Else the bacteria move towards the highest concentration of glucose, and consume it to gain more energy. A bacteria leaves a trail of chemical as it moves. A neutrophil, the first responder to an infection, then appears at the scene, recruiting other neutrophils to join in the fight. The neutrophils follow the chemical trail from the bacteria. Neutrophils leave a trail of immune chemicals which kill bacteria and gobble the bacteria up by phagocytosis if they get close enough. Later, macrophages appear at the scene which also release immune chemicals and gobble up bacteria. The macrophages are more effective at killing bacteria than neutrophils, but are slower to respond to the infection. Over time, the build-up of chemicals from the bacteria and immune cells damages the tissue. ## HOW TO USE IT Click the SETUP button to set up the infected wound. Click the GO button to start the simulation. The bacteria are green, the neutrophils are black circles with a red border, and the macrophages are larger black circles with a white border. Use the PATCH-VIEW dropdown to view glucose levels, bacterial chemicals, or immune chemicals. Glucose is shown in blue, while chemicals are shown in white. Before pressing SETUP, the model can be adjusted using a number of sliders: -If you want to change the number of bacteria initially introduced into the wound, use the INITIAL-BACTERIA-COUNT slider before pressing SETUP. -Similarly, the rate at which glucose is replenished from the bloodstream can be adjusted using the MAX-GLUCOSE-REPLENISHMENT-RATE slider. -The AVG-BACTERIA-CONSUMPTION-RATE slider controls how fast bacteria can consume glucose to gain more energy. -The IMMUNE-CHEMICAL-TOXICITY slider controls how effective the immune chemicals are at killing the bacteria, and the PHAGOCYTOSIS-RATE slider controls how fast the immune cells can gobble up bacteria. ## THINGS TO NOTICE Notice that as the bacteria reproduce, the concentration of the chemical they leave behind quickly increases. The immune system then responds after a short delay. With the PATCH-VIEW = CHEMICAL, you can see that the neutrophils and macrophages leave behind a trail of blue where they have depleted the white bacterial chemical and killed the neighboring bacteria. With PATCH-VIEW = IMMUNE-CHEMICALS, you can see that the neutrophils and macrophages leave behind a trail of their own chemicals seen as white or red. As the simulation runs, watch the MACROPHAGE RECRUITMENT COUNTDOWN for how long until the first macrophage appears. In the plot, although bacteria number (green line) decreases over time, tissue damage (red line) increases. When all bacteria are gone, the simulation stops. ## THINGS TO TRY Try increasing the number of initial bacteria in the wound using the INITIAL-BACTERIA-COUNT slider. How does this change the time it takes for the immune cells to remove all the bacteria? In diabetes, patients often have increased glucose levels in their blood. Try increasing the MAX-GLUCOSE-REPLENISHMENT-RATE slider to model how this affects the time required for the immune system to clear the bacterial infection. What does this tell you about how long healing takes for someone with diabetes compared to a healthy person? Diabetic patients also have immune systems which are less effective at fighting bacterial infections. Try decreasing the PHAGOCYTOSIS-RATE slider or decreasing the IMMUNE-CHEMICAL-TOXICITY slider to model how this affects the time required for the immune system to clear the bacterial infection. What does this tell you about how long healing takes for someone with diabetes compared to a healthy person? ## EXTENDING THE MODEL Try modifying the macrophage functions to include both M1 (proinflammatory) and M2 (proresolving) macrophage cell populations. M1 macropahges should have increased movement towards bacteria (function: move-to-bacteria) and increased phagocytosis of bacteria (function: phagocytose). The release of immune chemicals by M1s to kill bacteria (function: release-immune-chemicals) should increase tissue damage (function: increase-tissue-damage). However, M2 macrophages should have decreased movement toward bacteria and decreased phagocytosis of bacteria. They should release different immune chemicals which decrease tissue damage and inflammation and increase wound healing. Add complexity to the model by adding innate immunity's complement system. These new protein turtles should move toward bacteria and recruit the neutrophil immune cells rather than a chemical released from the bacteria themselves. The immune chemicals released by neutrophils and macrophages should then recruit more immune cells rather than the current countdown timer implementation. ## NETLOGO FEATURES The built-in diffuse primitive lets us diffuse the glucose, bacteria chemicals, and immune chemicals easily without complicated code. The built-in primitive die removes bacteria. The built-in primitive patches-in-radius allows bacteria and immune cells to sense the characteristics of neighboring patches. ## CREDITS AND REFERENCES Infections in patients with diabetes mellitus: A review of pathogenesis: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3354930/ Neutrophil function and metabolism in individuals with diabetes mellitus: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2007000800003&lng=en&nrm=iso&tlng=en @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 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count bacteria setup go count bacteria setup go count bacteria setup go count bacteria setup go count bacteria @#$#@#$#@ @#$#@#$#@ default 0.0 -0.2 0 0.0 1.0 0.0 1 1.0 0.0 0.2 0 0.0 1.0 link direction true 0 Line -7500403 true 150 150 90 180 Line -7500403 true 150 150 210 180 @#$#@#$#@ 0 @#$#@#$#@