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explain why there are differencess in the dz phenotypes of 
Xlinked SCID animals with mutation in their IL2 receptor gamma chain gene 
(common gamma chain gene) and animals with mutations in their IL2 gene 
(eg, IL2 knockout mice)


Xlinked scid isn't that common; other diseases 
are more common.
Notes are pretty complete about what we'll talk 
about...it's not her intent that you learn all this stuff on the slide, 
just hear the words and maybe in the future you will remember them. 


Primary Immunodeficiencies:
congenital, not acquired.

-predominant 
antibody defects (B cell)
-predominant defectss of cell mediated immunity 
(T cell)
-immunodeficiency associated with other defects (hematopoiesis, 
mphage)

Take home points:

combined deficiency usually means it affects 
both T and B cells
defects in many different genes can cause 
immunodeficiencies, only a few of those genes are known
a few of these 
defects have been found in humans; fewer in animals (but not zero)
these 
disease often show up when maternal antibodies wane (around weaning)

often, the only tx is Ig or bone marrow transplant (BMT)

knowing what 
the gene is is the best way to be able to detect the disease and 
therefore prevent it by not breeding carriers. this is useful. we can 
just take away reproductive rights of genetically defective animals. 
also, if you know enough about a disease you can get a better diagnosis 
early and hopefully help an affected animal. 

there are a lot of places 
for something to go wrong in immune system...
hematopoietic stem 
cells...growth factors, differentiating factors, colony stimulating 
factors, various cytokines involved in stimulating different 
lineages...all those cells that make cytokines and lymphokines and 
things. 

fairly complete list of immunodeficiencies in dogs and cats is 
in handout
selective IgA deficiency
Xlinked SCID
chediak-higashi sydrome

caine cyclic hematopoiesis- gray collie syndrome

some, we know gene 
defects for them
-Xlinked SCID
-leukocyte adhesion deficiency in cattle 
(BLAD)

SCID with adenosine deaminase deficiency - famous in people - 
this is the disease the first gene therapy trials were done for. this is 
clinically identical to SCID with ADA activity. both T and B defects - T 
lymphocytes accumulate toxic amounts of deoxyadenosine triphosphate and 
die off (b/c of enzyme deficiency) - B cell defect due to loss of T cell 
help.

Wiskott-Aldrich syndrome - x linked
defective Ab production to 
bacterial polysaccharides
all hematopoietic lineages are aafected.

mutations in WASP gene are present - function of gene unknown
defects in 
cellular cytoskeletal architecture and transmembrane signalling are 
present. 
so the disease is well characterized, but the underlying 
pathology is still confusing. 

Hyper IgM syndrome - xlinked
increased 
IgM, decreased other immunoglobulins
defect in T cell help
defect in 
ligand for B cell surface antigen CD40. so, soluble CD40 ligand which is 
absent from affected T cells is being tested in vitro as a possible 
treatment. 

Xlinked agammaglobulinemia - defect specifically in B cells- 
tyrosine kinase defect

LAD: leukocyte adhesion deficiency
characterized 
in human, Holstein cattle, and Irish Setters
-recurrent bacterial 
infections
-impaired wound healing
-reduced expression of B2 integrins on 
leukocytes
-due to mutations in CD18 gene

irish setter came in with sore 
on foot, big swollen lesion, but no pus. very high white count. gets 
better on abx. but keeps recurring. similar things in cows. in cows, and 
people, we know there is reduced expression of b2 integrins on leukocytes 
- CD18 is mutated. 

b2 integrins are required for neutrophils to 
extravasate - they interact with endothelial cell adhesion molecules. 
they consist of an alpha subunit and common b subunit which is the CD18 
chain. if you take lymphocytes from an affected dog, they won't adhere 
normally. 

cows with disease had assays for CD18 done - affected animals 
had no CD18 on surface of lymphocytes. they do have mRNA for it. there is 
an A->G substitution at nucleotide 383 causing protein degradation, in 
cattle. it was predicted that 0.2% of holsteins in USA would have this at 
birth. this was due to founder effect - common, popular sire used in this 
breed.  but, they know the mutation and can test for it now, so people 
are not breeding these animals. 

Irish setters - no one looked at the 
gene yet, so we don't know for sure what is going on with that.


Chediak-higashi syndrome: in many mammalian species - man, cattle, cat, 
killer whale. common features 
-decreased pigmentation in hair, eyes

-huge lysosomal granules in any granular cells such as PMN, melanocyte

-NK cell deficiency
-platelet problems
-susceptible to infections

-usually lethal
-"beige" bg mouse gene cloned
same gene defective in 
people
affected people have silverygrey hair. 
affected cow is white

man 
- grizzled hair, poor survival
hereford - ghost pattern hair, 
poorsurvival

cats - persians - blue smoke color with green/yellow iris. 
autosomal recessive. identical to dz seen in people and mice. 

another 
sort of common immune deficiency is the athymic/nude animal - various 
rodents, calves, Birman cats, guinea pig. severely immunodeficient 
animals, athymic, aplastic LNs, peyer's patches, spleen. 

nude mice:

athymic 
gene has been cloned - we think it is a transcription factor

defect is in a member of the winged-helix protein family (named after 
fruit fly research)
hairlessness due to improper keratinization of hair 
follicle

there are also some breed specific infection susceptibilities 
out there:

canine susceptibility to pneumocystis carinii
pneumonia at 6 
mos-1 yr.
usually lethal
most reports in miniature dachshunds
no 
increased susceptibility to other organisms!

k9 susceptibility to avian 
mycobacteriosus:
autosomal recessive in basset hounds
similar dz in 
mouse, human, cat

mouse susceptibility/Nramp1 - susceptible to multiple 
organisms

SCID mice - 
inability to produce mature, functional 
lymphocytes (T and B)
incorrect joining during V(D)J recombination
cells 
of these animals are very xray sensitive
DNA double-strand break repair 
defective
defect maps to gene for the catalytic subunit of DNA dependent 
protein kinase- a major enzyme involved in the double-strand break 
repair.

so it was determined that the VDJ recombination needs to use the 
DNA double-strand break repair pathway. 

while researching this, people 
were also looking at arabian horses.
SCID in arabians is probably carried 
by up to 25% of arabians.
these horses have no IgM, low lymphocyte count, 
and lymphoid tissue hypoplasia. tx BMT
usually lethal by 5 mos
defective 
VDJ recombination activity
defective DNA dependent protein kinase 
activity (5 base pair deletion; test is available so now we can get rid 
of this disease)

Canine X linked SCID:

this disease has a specific 
cause - but other mutations could cause a similar disease. this disease 
has helped us to learn about cytokines. in arabian horses, similar 
message - understanding VDJ recombination, double stranded break repair - 
several immunodeficiencies in mice resemble this, with lymphoid specific 
aspects - so different proteins in the same complex doing the same 
function exist, and a mutation in any one could result in similar 
disease. other components in this break repair pathway such as DNA 
binding subunits could be defective, another protein also exists that 
could be mutated and cause similar disease. so once you find a pathway 
you know where to  look for defects.

but with canine severe combined 
immune deficiency (X linked):
first seen in basset hounds here in the mid 
70s. 
affected puppies failed to thrive, were small, stunted
only males 
affected
affected animals have pyoderma, ear infections
hypoplastic 
peripheral LNs
absent thymic shadow on raads
at 6-8 wks: growth 
retardation, gastroenteritis, pneumonia, etc - 
death by 8-10 weeks.


clinical lab findings of x-linked SCID
lymphopenia, low IgG, 
low/undetectable IgA, depressed lymphocyte responses to mitogens (can't 
stimulate them with lymphocyte stimulation test), and lymphocytes fail to 
bind IL2. 

In people, X-linked SCID (boy in the bubble disease) is the 
most common immunodeficiency. it wasn't until 1993 that it was discovered 
that there is a particular defective gene -the common gamma chain gene. 
this is a component of the IL2 receptor. this is part of the receptors 
for multiple interleukins - IL2, IL4, IL7, IL9 and IL15. that helps to 
explain why this is such a severe immunodeficiency. 

if you knock out 
IL2 gene, you do not have SCID mice. mice are ok, but sometimes have 
inflammatory bowel disease. also if you knock out IL4, you don't cauase 
SCID. but you knock out this gamma chain gene - you lose function of all 
the cytokines that have receptors with this gamma chain in it. 

the 
gamma chain being a component of multiple receptors explains a lot, then. 
this is the exam question!

you can imagine, we were pretty sure the same 
disease in these dogs was the problem. they looked at the dogs - first 
thing was to find normal sequence- realize, you not only all have the 
same genes, the genes are very similar. this gamma chain gene is 84% 
identical b/w dogs and people. that's typical - closer than mouse and 
human.

there was a 4bp deletion found causing a premature stop. 
once 
you find the mutation you can find the carrier animals. 

in 1993, other 
dogs showed up with similar dz - 
bruiser, 7 wk old Corgi
at 13 wks, 
looked awful
owned by LVMD. signs: pasty white stool, mainly. vet did GI 
biopsies, found nothing, referred him here. it turned out a relative of 
his had been here 3mos before with pyoderma, hypoplastic LNs, low IgG, 
lymphopenia, etc. he'd collapsed in hypovolemic shock a few times and was 
euthanised. 
so they looked at bruiser closely - everything was just like 
in the Xlinked SCID basset hounds. so, they checked to see if his 
lymphocytes bound IL2 - they did not. 

so they looked at his genes - he 
was  missing a base pair, and had a premature stop codon resulting in a 
nonfunctional protein. this was fun from the genetics point of view (not 
the dog point of view) b/c the breeders were great...they came here and 
plotted out pedigrees, and submitted samples from all suspected carrier 
females - they were able to go back and find the original mutation in the 
grandparent of this dog. so it didn't spread very far at all.

with 
xlinked dz, you do often see the dz within a few generations. with 
autosomal recessive diseases, it takes longer unless you do 
brother/sister breedings and stuff.

the dog with the spontaneous 
mutation, btw was named BooBoo :)

another interesting thing in people 
that mimics Xlinked SCID but was seen in a girl....there are kinase 
domains in these receptors. this girl was homozygous for a mutation in 
the gene for one of the kinases. so she had the same phenotype but a 
different underlying problem. 


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