general pathology: immunodeficiency and transplantation

General Pathology:General Pathology:Immunodeficiency and Immunodeficiency and

TransplantationTransplantationLorne Holland, M.D.Lorne Holland, M.D.

Lorne.Holland@ucdenver.eduLorne.Holland@ucdenver.edu

Immunodeficiency

• A failure of the immune system to respond to usual stimuli

• Causes are varied, but can be grouped into defects of humoral immunity, cell-mediated immunity, phagocytosis and complement

• May be inherited (primary) or acquired (secondary)

Humoral Deficiencies• Infancy

– At birth, essentially all circulating immunoglobulins are maternal IgG

– As infant ages, maternal immunoglobulins are removed from circulation

– At the same time, baby is ramping up production of its own immunoglobulins (IgG, IgM, IgA)

– Early on, the decline in maternal concentrations happens a little faster than the infant can synthesize new immunoglobulins

– Around 3-6 months synthesis rates increase and total immunoglobulin concentrations begin to rise

Humoral Deficiencies

• X-linked agammaglobulinemia (Bruton’s)– Failure of precurssor cells to differentiate

into B-cells because of a lack of Bruton’s tyrosine kinase

– Responsible defective gene on X chromosome

– Initally present with recurrent pyogenic (bacterial) infections between 4 months and 2 years

– Replacement (transfusion) of pooled immunoglobulin can treat

– Increased risk of autoimmune diseases

Humoral Deficiency• Hyper IgM syndrome

– Normal or elevated levels of IgM, but no other immunoglobulins

– Most often, lack of CD40 ligand on T-cells leads to no isotype switching by B-cells and poor stimulation of macrophages

– CD40L is located on X chromosome so 70% of cases are seen in males

– Recurrent pyogenic infections and Pneumocystis pneumonia

– Treat with pooled immunoglobulin and prophylactic antibiotics or BMT

Humoral Deficiency

• Selective IgA deficiency– Normal or high immunglobulin

concentrations expect IgA which is low or completely absent

– Typically clinically silent though those with no IgA may have increased rates of respiratory and GI infections

– Those with no IgA may also have anaphylactic reactions to IgA in blood products

– At higher risk for developing autoimmune diseases

Humoral Deficiency

• Common variable immunodeficiency– Low concentrations of one or more kind

of immunoglobulin– Usually much more modest increase in

rate of pyogenic infections and so may not be diagnosed until adulthood

– Also at increased risk for a number of autoimmune diseases and lymphoid malignancies

Cell-mediated Deficiency• Severe combined immunodeficiency

– Impaired T-cell function which can also cause secondary impaired B-cell function

– Autosomal recessive form due to mutations in cytokine receptors which stimulate growth (25%)

– X-linked form due to mutation in adenosine deaminase necessary for DNA synthesis (50%)

– Present in the first weeks or months of life with recurrent infections of all kinds

– In absence of BMT (or gene therapy), life expectancy is typically 1-2 years

Cell-mediated Deficiency• Thymic hypoplasia (DiGeorge syndrome)

– Underdevelopment (absence) of the thymus leaves few places for T-cells to be “educated”

– Despite this, immunodeficiency is typically rather mild except in total absence

– Susceptible to fungal, viral, and protozoal infections (not typical bacteria species)

– Death can occurs due to associated abnormalities (e.g. cardiac malformations)

– Maybe prophylaxis with sulfamethoxazole/ trimethoprim (Bactrim, Septra)

– Transplantation of thymic tissue may be helpful

Cell-mediated Deficiency• Wiscott-Aldrich syndrome

– Defects in both T-cells and B-cells along with thrombocytopenia and eczema

– Exact mechanism is unknown, but responsible gene is on the X chromosome and codes for proteins involved in cytoskeletal structure

– Untreated, death in early childhood– BMT is only effective treatment– Increased risk of hematologic malignancies

Phagocytosis Deficiency• Chronic granulomatous disease

– Failure of neutrophils to produce sufficient amounts of bacteriocidal products (reactive oxygen species) after phagocytosis

– Typically, presents as severe, recurrent skin infections by bacteria (staph) or fungus (candida, aspergillus) and/or pneumonia

Phagocytosis Deficiency• Chronic granulomatous disease (cont)

– Ultimately, spreads systemically and form abscesses and granulomas in multiple organs (liver, bones)

– Maybe prophylaxis with sulfamethoxazole/ trimethoprim (Bactrim, Septra)

– Aggressive, early treatment of any potential infections

– Interferon therapy (may increase amounts of bacteriocidal products synthesized)

Complement Deficiency

Complement Deficiency

• C1, C4 and/or C2 present with autoimmune symptoms

• C3 presents with severe, recurrent bacterial infections (convergence of classic and alternate pathways as well as chemotaxis, opsonization)

• C5, C6, C6, C8 (MAC) presents with recurrent infections (meningitis, sepsis, arthritis) with encapsulated bacteria (Neisseria sp.)

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– Caused by the human immunodeficency

retrovirus (RNA)– Two proteins on outside gp120 and gp41– Inside: p24, RNA, protease, reverse

transcriptase, integrase– Three key retroviral genes: gag, pol and

env – These gene products (proteins) must be

cleaved by protease to become functional

HIV structure

p24

gag, polenv

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– Virus adheres to cells via interaction of

gp120 and CD4 with help from chemokine receptors (CXCR4 and/or CCR5)

– T-cells, macrophages and other APCs are most vulnerable

– gp41 penetrates membrane and allows for transfer of viral RNA

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– Viral RNA reverse transcribed into DNA– Viral DNA is inserted into host DNA by

integrase– Inserted DNA remains latent until

infected cell is stimulated (by normal means) and begins to divide

• http://www.youtube.com/watch?v=9leO28ydyfU

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– Acute infection causes flu-like symptoms in

some, but not all people– Although destruction of CD4+ cells is

occurring, symptoms may not appear for several years

– Time to seroconversion depends on testing method•Typical anti-HIV antibody screens ~3 weeks• HIV p24 antigen ~2 weeks•HIV RNA ~1 week

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– After latent phase, clinical manifestations vary– Generalized lymphadenopathy, diarrhea, night

sweats, weight loss– Meningitis, encephalopathy, neuropathy, dementia– Unusual, opportunistic infections- Pneumocystis

pneumonia, severe CMV or HSV, cerebral toxoplasmosis, unusual mycobactrial species, unusual fungal species, GI cryptosporidum

– Tumors- Kaposi’s sarcoma (HSV 8), non-Hodkins lymphoma (EBV), cervical cancer (HPV)

Secondary Immunodeficiency

• Acquired Immunodeficiency Syndrome– Treatment options

•Nucleoside reverse transcript inhibitors•Non-nucleoside reverse transcript

inhibitors•Protease inhibitors•Entry/fusion inhibitors (gp120, gp41,

chemokine receptors)•Integrase inhibitor

Pneumocystis pneumonia

HSV and Kaposi’s Sarcoma

Toxoplasmosis and Cryptosporidium

Secondary Immunodeficiency

• Either due to loss of immunoglobulins– Nephrotic syndrome– Protein-losing enteropathy

• Or due to impaired synthesis of immunoglobulins and/or cells– Severe malnourishment– Destruction of bone marrow (e.g.

lymphoproliferative disorders)– Viral infections (CMV, measles, mono, et

al.)– Iatrogenic immunosuppression

Organ Transplantation

• Normal immunity helps protect the body from invasion by microorganisms and provides surveilance for development of cancer

• These same defense mechanisms will attack “foreign” transplanted tissue

Organ Transplantation

• Successful organ transplantation requires – Sufficient pharmacologic suppression of

the immune system to prevent rejection– Without oversuppression which would

predispose patients to opportunistic infections, tumors and graft-versus-host disease

Organ Transplantation

• Human leukocyte antigens (HLA), a.k.a MHC proteins, are strongly antigenic

• One gene is inherited from each parent for each HLA class (MHC I- A, B, C and MHC II- DP, DQ, DR)

• So a cell may express up to 12 different HLA proteins

• A, B and DR are the most important

Before Transplantation

• Find organ donor who matches as many HLA alleles as possible

• Depending on organ, may need to use ABO (blood type) compatible organ as well

• Screen recipient for presence of existing antibodies to foreign HLA types

• Find suitable live donor (kidney, liver, lung, bone marrow) or cadaveric donor (above plus heart, pancreas)

After Transplantation• Immunosuppression with one or more drugs

– Cyclosporine & tacrolimus- blocks action of the phosphatase (caclineurin) which normally turns on IL-2 production

– Sirolimus- blocks action of a kinase necessary for T-cell proliferation (and activation)

– Azathioprine & mycophenolate inhibit DNA synthesis

– Monoclonal antibodies (end in “ab”, Muromonab) bind to T-cell proteins and lead to destruction by other immune cells or bind to and block IL-2 receptor

– Corticosteroids increase synthesis of proteins which inhibit transcription of multiple cytokines (IL-2, et al.)

After Transplantation• Monitor for rejection

– Hyperacute antibodies to proteins on transplant are present at time of transplantation, rapid destruction (within minutes to hours) of transplantion

– Acute failure of immunosuppression so that antibodies develop in the weeks or months following transplantation

– Chronic immunosuppression can not (yet) be perfect, small amounts of damage accumulate over years and eventually destroy transplant

After Transplantation• Rejection, direct

– Donor APCs do what they do, but interact with recipient CD4 T-cells which have entered the transplant

– Recipient CD4 cells recognize MHC II on donor APCs as foreign

– CD4 cells recruit (cytotoxic) CD8 T-cells and B-cells (which differentiate into plasma cells and make antibodies)

– CD8 cells mediate cytotoxicity via foreign MHC I (which is on all nucleated cells, importantly endothelial cells)

After Transplantation

• Rejection, indirect– Donor HLA antigens either enter the

blood stream or are carried by donor dendridic cells (APCs) to recipient lymphoid tissue

– Recipient CD4 T-cells recognize the foreign antigens, enter circulation, find their way to the transplant, and cause inflammatory response

– Again, damage to endothelium is as important as damage to organ itself

Graft-versus-host Disease

• Highest risk after BMT, but can occur after any transplant, including transfusion

• Donor lymphocytes in the transplant or transfusion recognize the recipient as foreign, but the recipient fails to recognize the donor lymphocytes as foreign

• The recipient lymphocytes fail to act either because the donor cells do not look foreign to them or they are defective in number or function

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Graft-versus-host Disease

• Any tissue can be affected, but liver, skin and GI tract are particularly affected

• Present with jaundice, rash and/or bloody diarrhea

• May be acute with rapid increase of symptoms or chronic with insidious progression

• Treat with increased immunosuppression and/or immunomodulation (photopheresis)

Questions?