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immune complex dz - type III
delayed (cell mediated) hypersensitivity type IV

type III: immune complex disorders, arthus. deposits of Ag/Ab complexes 
activates complement, resulting in inflammatory rxn. one type is arthus 
rxn: localized situation. another type is "serum sickness" more systemic. 
both are persistence of Ag along with formation of Ab are resulting in 
complex formation

Type IV: cell mediated - lymphokines from t cells recruit macrophages. 
contact sensitivity, etc.

so. type III. Ag and Ab always form complexes. these complexes are 
usually removed from circulation no problem and nothing happens. but if 
there is persistence of Ag, in circulation or locally, and complement is 
fixed, you get activation of inflammatory response.

Arthus (a kind of type III rxn). this was discovered by french guy named 
Arthus who injected an Ag into rabbits repeatedly at 3-4 wk intervals to 
see how high an Ab response he could get. after about 6 injections, 
animal got a swelling 4-6 hrs after injection, and after about 7 or 8 
shots, the skin there would necrose and slough off. normally you'd expect 
about 14 days to get Ab level up, and then you keep doing this, and you 
keep getting repeated secondary responses. but here we're getting this 
localized acute inflammatory rxn. histologically, the walls of small 
blood vessels become totally infiltrated by neutrophils, and bv wall is 
destroyed, and that results in the lumen of the bv getting thrombotic and 
the tissue will slough since no blood supply. there is also a lot of Ig 
in the wall of the blood vessel...there is Ag/Ab complex deposited there.


basically, if you ahve an individual hyperimmuninzed, whith very high IgG 
level, a small amt of that would normally get into vessel walls. but, 
when you come along and keep injecting Ag locally, you keep forming 
immune complexes, fixing complement, and by the time youget to C3, you 
start getting anaphylatoxins, which draw in PMNs (neuts), and PMNs 
breakdown normally in 24-48 hrs in tissue. but they come in and try to 
eat up the Ag/Ab complexes, but aren't good at it, but they end up 
liberating a lot of lysosomal enzymes. so this frustrated attempt at 
eating the complexes causes destruction of the vessel wall. also there's 
another cell at least marginally playing a  role. all along small blood 
vessels are mast cells and a few basophils in circulation. when the mast 
cells get triggered to release histamine, the gaps between endothelial 
cells get bigger (endo cells contract apart from each other) allowing 
more complexes into the vessel wall. so if you think this trhough, it's 
pretty straightforward. end result: destruction of vessel wall. PMNs and 
complement are crucial to this event. if you give cobra venom to tieup 
all the complement, you can't get an arthus rxn to form. also if you 
remove all neutrophils you can't get an arthus rxn to form. also 
platelets release vasoactive amines that act like histamine. so as 
platelets start clumping you start having that effect as well.

mechanism of inflammation
anaphylatoxins
chemotaxis of neuts
phagocytosis
vasoactive amines
cytolysis (lysosomal enzymes)

Now, the systemic counterpart is serum sickness. why? well, you have 
antigenic sensitization as before. 

50 yrs ago, if you ran into a barbed wire fence they worried about you 
getting tetanus. so they gave you 50 cc horse serum containing tetanus 
antitoxin, but they didn't filter out the horse proteins. so the body has 
to get rid of all these foreign proteins. dr weber had this problem once. 


so 10-14 days after injection you start making Ab. then you get fever, 
swollen LN, splenomegaly, feel sick. what happens is, you get this huge 
amt foreign protein injected at point x. the amount of free antigen 
gradually declines over the first week as reticuloendothelial system 
deals with it, then you start having antibody production between about 
day 9 and day 12 - and you start having deposition of immune complexes in 
kidney, joints, skin, etc. kidney is often very affected. when there are 
few antibodies and lots of ag, complexes are small. when there is a lot 
of free antibody, complexes get larger. the smaller ones are more 
dangerous because they are deposited more easily. larger ones are 
filtered and eliminated more easily. 

again, this is provoked by persistence of antigen while making antibody. 


so what happens in the glomerulus?
you have ag/ab complex fom, and complement is fixed and platelets and 
basophils become involved and because complexes can bind to them, they 
will release vasoactive amines leading to contraction of endothelial 
cells which open the gaps between the endo cells, causing leaky 
capillaries.

small complexes go under the basement membrane (BM) and get through it 
and localize between the BM and the podocytes of the tubular epi cells, 
and bigger ones get trapped between endo cells and BM. eventually, the 
glomerulus is destroyed to a large extent. survival depends on a number 
of things. 

why is more stuff deposited in glomerulus? why not elsewhere? turbulence 
is high in glomerulus, and BP compared to rest of body is also very high 
in glom. those factors (turbulence, increased BP) lead more readily to 
deposition of immune complexes. also  we know there are some immune dzs 
which produce complexes that preferentially localize in glomerulus - eg, 
SLE (systemic lupus erythematosis, where you make Ab to your own DNA). 
whereas rheumatoid arthritis immune complexes localize in the joints.

+charged complexes localize in kidney (glom cells -charge.), in general.
now, every time you have immune complexes formed in circulation, you 
don't die.
whether or not you get complex deposition depends on a few things.

the critical part is concentration of complexes - if only a few, wont' 
destroy the whole kidney. second thing is size of complexes. small and 
intermediate ones more likely to deposit; larger ones removed by 
reticuloendothelial system. also, the isotype is a factor: IgG is more 
dangerous than IgM, which is more easily removed by reticuloendo system. 
and charge is important.

note whenever you have Ag in sl. excess to Ab, that is more predisposing 
to immune complex deposition, because you then tend to make smaller 
complexes. so ratio about 2:1 Ag:Ab is prime. if ratio reverse, you get 
big complexes, and not as much deposition.

now, a minor case of this will survive, but a severe or longstanding case 
eg with lupus will be fatal due to chronic renal failure as more and more 
glomeruli are destroyed. you get a glomerular nephritis and die. yuck.

so same thing as before, like arthus rxn. not a big deal if complexes are 
between epi and BM or endo and BM, either way destroys glomerulus.

if you look histologically, between endo and BM is large mass of black 
Ag/Ab complex. it's really ugly looking.

from a pathologist's standpoint, when you take a bx of kidney suspected 
of this dz, you see a lumpy, bumpy, peculiar pattern, showing the uneven 
deposition of immune complexes. this is very characteristic of immune 
complex dz.

recall the bigger the complex, the easier it is to clear it w/o it 
depositing. smaller complexes deposit more readily and are harder to 
clear. the presence of complement in plasma normally keeps complexes 
small. folks w/complement deficiencies get large complexes.

a crucial point in terms of animals. we're talking about persistence of 
Ag...what kind of Ag persists in the circulation? don't have to remember 
these all but realize some key things.

in dog...pyometra - lots of bacteria persist in uterus; SLE - dog's DNA 
persists, of course. adenovirus I, dirofilariasis, bacterial 
endocarditis, ehrlichiosis, neoplasia (tumor antigen) - all of these 
antigens will be persistent and can be associated w/immune complex dz. 
note can be bacteria, parasite, endogenous, tumor antigen, virus, etc.

in cat: FeLV, hemopoietic neoplasms, SLE, FIP, pancreatitis
in bovine: bovine viral diarrhea
equine: EIA
swine: hog cholera

so persistence of Ag can be a host of underlying disease processes. you 
only get immune complex dz when Ag and Ab are in right ratio to each 
other and other conditions aremet. it's actually relatively rare. we may 
all get small bouts of it during viral infxn, but it may be entirely 
subclinical.

the book has good info on this and is good and precise and pretty short

one other thing you can see in animals and man which causes an organ 
specific immune complex dz - slide: cat lung - normal, pink, shiny. 
what would cause arthus type rxn in lung? well, when lung is constantly 
exposed to Ag. what kind of Ag? fungal Ag, mold, things you inhale that 
are antigenic. eg in horses COPD can involve immune complex dz. in 
humans, farmers who work in silos would get this from inhaling fungal 
spores and becoming sensitized, and then getting alveolitis when they 
went back into the silo: "farmer's lung". also people who worked on 
thatched roof, or cheese washer's disease - cheese people worked in 
caves, lots of spores hanging around. so these are all caused by 
persistence of antigen, and via the same mechanisms discussed before. why 
wouldn't a person w/farmer's lung get immune complex disease? because the 
spores remain localized in the lung, so complexes do not circulate but 
rather stay in lung. that's why you get arthus type of rxn.

next, type IV, delayed hypersensitivity. dr scott has already discussed 
CMI. the tuberculin type rxn is really a test situation, and what we're 
trying to do is to test if an animal has already been exposed to the TB 
bacillus. TB is poorly phagocytosed, often persists in macrophages,hard 
to get rid of and clear from body - leprosy also acts this way, as does 
brucellosis, syphillis. 

assume you have animal that was exposed to TB. you'd expect that animal 
to have a lot of CD4+ T memory cells. you have initial exposure, and what 
happens? langerhans cells trigger the Th1 cells, and they expand in LNs 
and circulate as sensitized T cells. then you inject your antigen, and 
you get the memory T cells comng over, and your Th1 cells are triggered, 
and they liberate (MUST KNOW) IL2, IFNg, TNF, and so on. this is crucial. 
the TB rxn is almost exclusively mediated by these cytokines. IFNg is a 
big one as is TNF. they upregulate the adhesion molecules on endo cells, 
allowing more WBC to adhere locallly, so they infiltrate the site, you 
get a huge influx of mostly mononuclear cells - 80% monocytes, most of 
the rest Th1 cells. s you have lots of TH1 and macrophages causing this 
hard swellign in the skin where the Ag was injected. rxn peaks at 48-72 
hrs. this is why it's called DELAYED hypersensitivity. is a cell mediated 
rxn where Th1 cells release cytokines bringing in mphages.

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slide: positive TB test; histological slide: shows all mononuclear cells

note: when you test positive, it doesn't mean you have a fulminating TB 
infection. you have simply been EXPOSED to it - could have been 
vaccinated for it or something. could have an old, healed tubercle. 
humans who test positive are tested further and treated as needed. 
animals that are positive are generally euthanised for public health 
reasons.

this cell mediated immunity involving TH1 cells...antigen comes in skin, 
you have the Th1 cells secreting cytokines, calling in mphages, which 
release lysogenic products to digest and kill organism. ultimate effector 
cell in terms of getting rid of organisms is the macrophage, which is 
owrking under influence of cytokines released by the main mediator cell, 
the Th1 cell.

slide: big ugly liver with TB nodules - small granulomas. entire lung is 
destroyed by coalesching TB lesions. when there is extensive involvement 
of this response, it can lead to complete destruction of the tissue. 
these are granulomas - see poster in MDL 11. the granulomas are interplay 
between immune system and cellular rxn going on as healing tries to take 
place. it's different from a tuberculin rxn. it leads to some other cell 
types showing up histologically.

another cell mediated type of rxn a bit different from tuberculin rxn is 
CONTACT SENSITIVITY eg poison ivy. poison ivy isn't an allergy, it's a 
contact sensitivity. slide: wristwatch sensitivity - under the buckle an 
erythematous, swollen and crusty lesion forms. to test what sensitivity 
is to, you make patches incorporating various compounds and apply them to 
the skin. after about 48 hrs you will get "positive patch test" - peaks 
at 48-72 hrs. so again, it is DELAYED hypersensitivity involving the cell 
mediated response.

histologically you have microvesicles and edema showing up in epidermis, 
and a mononuclear infiltration of the dermis. also hyperemia in the 
dermis. the blister formation in the epi layer is a function of location 
in skin (?what?)

what's really going on...most soaps, dyes, metals that contact skin are 
basically thought of as haptens. metals are ions but will chelate in 
tissue with some protein and make carrier complex. hapten complexes are 
picked up by langerhans cells. we're not sure what lang. cell does with 
it, but it migrates through lymphatics into the LN paracortex and 
presents Ag to CD4+ Th1 cells. these cells proliferate and circulate and 
now youhave a sensitized individual. then you have a reexposure (or 
continuous exposure) and the sensitized t cells contact the langerhans 
cells and immediately start making cytokines - IFNg, IL2, TNF. TNF can 
upregulate with IFNg adhesion molecules on endothelium, allowing more WBC 
to adhere and migrate to area. notice again this is almost exclusively a 
cellular response.

antigen specific memory t cells = Th1 cells.

your keratinocyte itself, when stimulated by cytokines, produces its own 
cytokines upregulating MHCII, helping TH1 cells proliferate, and make 
IL2.

how does this all stop? eventually if you eliminate the exposure to the 
hapten eg if  you don't keep wearing that cosmetic or you stop wearing 
the watch or whatever, you have less exposure. also the hapten carrier 
complexes are gradually metabolized and removed. also the keratinocytes 
make PGE which inhibits Th1, and makes TGFb which downregulates the Th1 
cells. so contact sensitivity is a cell mediated reactionn similar to 
tuberculin sensitivity, except you are dealing with haptens that must be 
complexed in tissue to become antigenic. in tb, you have a full fledged 
Ag involved.

delayed type hypersensitivy DTH types

contact - 48-72 hrs - eczema. infiltration of lymphocytes and 
macrophages, epidermal edema, keratinocyte involvement
tuberculin - 48-72hrs - local hardening and swelling. infiltration of 
lymphocytes, monocytes and macrophages. no keratinocyte involvement. test 
only.
granulomatous - 4 wks - hardening, eg in skin or lung

ch. 25...inflammation slide

type I wheal and flare immediate hypersensitivyt - matter of minutes - 
eosinophils - fast arrival and fast resolution. eg, hives.
IgE, mast cells, vasoactive amines.

type III immune complex, arthus. 4-8 hrs after exposure of 
hypersensitized individual. hemorrhagic rxn. neutrophils. 

type IV tb...peaks at 24-48 hrs, indurated and erythematous rxn.

so, to summarize DTH...

TH1 mediated
mediated by release of cytokines, IFNg, IL2, mphage chemotactic factor, 
TNF, etc
several variants of it.

this is all perfectly clear to everyone, because no one is asking any 
questions :)

ok, one question. when people discuss the nephron, what do they mean? a 
nephron starts w/glomerulus and ends at renal pelvis. it's the functional 
unit of the kidney. there's a blood part and a tubular part.

one additional thing. usually when people speak of cmi, they get 
confused. there is another thing called CMI - often it means somethign 
that is just mediated by cells and not antibodies. but you have to 
specify what cell you mean. most people today when you say CMI they think 
TH1 mediated, liberation of cytokines, activation of macrophages. this is 
CM-DTH type rxn. now, what do you call destruction of a virus infected 
cell or a tumor cell - any target cell. what cells are involved?  mostly 
CD8+ are responsible for killing virus infected cells. this doesn't 
involve the other factors above. it is cellmediated but it isn't what 
most mean when they say CMI. your CD8 T cell recognizes hte viral peptide 
w/MHCI and proliferates into Tc cells. the Th1 cells provide IL2 to help 
the Tc cells proliferate. you also get Th2 cells helping B cells make Ab. 
now how does Tc cell kill the target cell? direct contact. Tc recognizes 
MHCI + viral peptide and gives a "lethal hit" during intimate cell-cell 
contact. Tc releases perforins which make a hole in target cell membrane.


notice that during the "intimate cell to cell contact" a number of 
adhesion molecules on surfaces ofboth cells interact. there is firm 
adhesion whch takes place quickly - 2 to 10 min; then during 30 min to a 
couple hrs the perforins are released. the lymphocyte doing this is not 
killed in the process. it can repeat the process several times. the 
actual killing occurs via preformed perforins released from the Tc cell's 
interior.

note: transcriptions have been very good, perhaps better than the 
lectures. but note there is another handout for next time.

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