Unit 4 Part 6 Human Immunodeficiency Virus

1. Unit 4Part 6 Human Immunodeficiency Virus Terry Kotrla, MS, MT(ASCP)BB

2. Introduction • Etiologic agent of Acquired Immunodeficiency Syndrome (AIDS). • Discovered independently by Luc Montagnier of France and Robert Gallo of the US in 1983-84. • Former names of the virus include: • Human T cell lymphotrophic virus (HTLV-III) • Lymphadenopathy associated virus (LAV) • AIDS associated retrovirus (ARV)

3. Introduction • HIV-2 discovered in 1986, antigenically distinct virus endemic in West Africa. • One million people infected in US, 30 million worldwide are infected. • Leading cause of death of men aged 25-44 and 4th leading cause of death of women in this age group in the US. • Reduced mortality resulting from the use of highly active antiretroviral therapies is a major factor contributing to the number of persons in the United States living with HIV disease. • Additionally, more than 56,000 new HIV infections are estimated to occur annually

4. HIV in the US

5. Characteristics of the virus • Icosahedral (20 sided), enveloped virus of the lentivirus subfamily of retroviruses. • Retroviruses transcribe RNA to DNA. • Two viral strands of RNA found in core surrounded by protein outer coat. • Outer envelope contains a lipid matrix within which specific viral glycoproteins are imbedded. • These knob-like structures responsible for binding to target cell.

6. Characteristics of the virus

7. HIV • The outer shell of the virus is known as the Viral enevlope. • Embedded in the viral envelope is a complex protein known as env which consists of an outer protruding cap glycoprotein (gp) 120, and a stem gp14. • Within the viral envelope is an HIV protein called p17(matrix), and within this is the viral core or capsid, which is made of another viral protein p24(core antigen).

8. Structural Genes • Three main structural genes: • Group Specific Antigen (Gag) • Envelope (Env) • Polymerase (Pol)

9. Group Specific Antigen (Gag) • Located in nucelocapsid of virus. • Icosahedryl capsid surrounds the internal nucleic acids made up of p24 andp15. • p17 lies between protein core and envelope and is embedded in the internal portion of the envelope. • Two additional p55 products, p7 and p9, are nucleic acid binding proteins closely associated with the RNA.

10. Envelope (Env) • Envelope (Env) gene codes for envelope proteins gp160, gp120 and gp41. • These polyproteins will eventually be cleaved by proteases to become HIV envelope glycoproteins gp120 and gp41. • gp160 cleaved to form gp120 and gp41. • gp120 forms the 72 knobs which protrude from outer envelope. • gp41 is a transmembrane glycoprotein antigen that spans the inner and outer membranes and attaches to gp120. • gp120 and gp41 both involved with fusion and attachment of HIV to CD4 antigen on host cells.

11. Polymerase (Pol) • Polymerase (Pol) codes for p66 and p51 subunits of reverse transcriptase and p31 an endonuclease. • Located in the core, close to nucleic acids. • Responsible for conversion of viral RNA into DNA, integration of DNA into host cell DNA and cleavage of protein precursors.

12. Viral Replication • http://tinyurl.com/3425m69 • First step, HIV attaches to susceptible host cell. • Site of attachment is the CD4 antigen found on a variety of cells • helper T cells • macrophages • monocytes • B cells • microglial brain cells • intestinal cells • T cells infected later on.

13. Early Phase HIV Infection • In early phase HIV infection, initial viruses are M-tropic. Their envelope glycoprotein gp120 is able to bind to CD4 molecules and chemokine receptors called CCR5 found on macrophages

14. Viral Replication • In late phase HIV infection, most of the viruses are T-tropic, having gp120 capable of binding to CD4 and CXCR4 found on T4-lymphocytes.

15. Viral Replication • The gp120 protein on virus binds specifically to CD4 receptor on host cell with high affinity. • Gp41 causes fusion of the virus to the cell membrane. • After fusion virus particle enters cell. • Viral genome exposed by uncoating particle.

16. Viral Replication • Reverse transcriptase produces viral DNA from RNA. • Becomes a provirus which integrates into host DNA. • Period of latency occurs.

17. Viral Replication • After a period of latency lasting up to 10 years viral replication is triggered and occurs at high rate. • CD4 cell may be destroyed in the process, body attempts to replace lost CD4 cells, but over the course of many years body is unable to keep the count at a safe level. • Destruction of large numbers of CD4 cause symptoms of HIV to appear with increased susceptibility to opportunistic infections, disease and malignancy.

19. HIV (arrows) Infecting a T-lymphocyte

20. Viral Replication • Methods of transmission: • Sexual transmission, presence of STD increases likelihood of transmission. • Exposure to infected blood or blood products. • Use of contaminated clotting factors by hemophiliacs. • Sharing contaminated needles (IV drug users). • Transplantation of infected tissues or organs. • Mother to fetus, perinatal transmission variable, dependent on viral load and mother’s CD 4 count.

21. Transmission

22. Primary HIV Syndrome • Mononucleosis-like, cold or flu-like symptoms may occur 6 to 12 weeks after infection. • lymphadenopathy • fever • rash • headache • Fatigue • diarrhea • sore throat • neurologic manifestations. • no symptoms may be present

23. Primary HIV Syndrome • Symptoms are relatively nonspecific. • HIV antibody test often negative but becomes positive within 3 to 6 months, this process is known as seroconversion. • Large amount of HIV in the peripheral blood. • Primary HIV can be diagnosed using viral load titer assay or other tests. • Primary HIV syndrome resolves itself and HIV infected person remains asymptomatic for a prolonged period of time, often years.

24. Clinical Latency Period • HIV continues to reproduce, CD4 count gradually declines from its normal value of 500-1200. • Once CD4 count drops below 500, HIV infected person at risk for opportunistic infections. • The following diseases are predictive of the progression to AIDS: • persistent herpes-zoster infection (shingles) • oral candidiasis (thrush) • oral hairy leukoplakia • Kaposi’s sarcoma (KS)

25. Oral Candidiasis (thrush)

26. Oral Hairy Leukoplakia • Being that HIV reduces immunologic activity, the intraoral environment is a prime target for chronic secondary infections and inflammatory processes, including OHL, which is due to the Epstein-Barr virus under immunosuppressed conditions

27. Kaposi’s sarcoma (KS) • Kaposi’s sarcoma (shown) is a rare cancer of the blood vessels that is associated with HIV. It manifests as bluish-red oval-shaped patches that may eventually become thickened. Lesions may appear singly or in clusters.

28. AIDS • CD4 count drops below 200 person is considered to have advanced HIV disease • If preventative medications not started the HIV infected person is now at risk for: • Pneumocystis carinii pneumonia (PCP) • cryptococcal meningitis • toxoplasmosis • If CD4 count drops below 50: • Mycobacterium avium • Cytomegalovirus infections • lymphoma • dementia • Most deaths occur with CD4 counts below 50.

29. Other Opportunistic Infections • Respiratory system • Pneumocystis Carinii Pneumonia (PCP) • Tuberculosis (TB) • Kaposi's Sarcoma (KS) • Gastro-intestinal system • Cryptosporidiosis • Candida • Cytomegolavirus (CMV) • Isosporiasis • Kaposi's Sarcoma • Central/peripheral Nervous system • Cytomegolavirus • Toxoplasmosis • Cryptococcosis • Non Hodgkin's lymphoma • Varicella Zoster • Herpes simplex • Skin • Herpes simple • Kaposi's sarcoma • Varicella Zoster

30. Infants with HIV • Failure to thrive • Persistent oral candidiasis • Hepatosplenomegaly • Lymphadenopathy • Recurrent diarrhea • Recurrent bacterial infections • Abnormal neurologic findings.

31. Immunologic Manifestations • Early stage slight depression of CD4 count, few symptoms, temporary. • Window of up to 6 weeks before antibody is detected, by 6 months 95% positive. • During window p24 antigen present, acute viremia and antigenemia.

32. Immunologic Manifestations • Antibodies produced to all major antigens. • First antibodies detected produced against gag proteins p24 and p55. • Followed by antibody to p51, p120 and gp41 • As disease progresses antibody levels decrease.

33. Immunologic Manifestations • Immune abnormalities associated with increased viral replication. • Decrease in CD4 cells due to virus budding from cells, fusion of uninfected cells with virally infected cells and apoptosis. • B cells have decreased response to antigens possibly due to blockage of T cell/B cell interaction by binding of viral proteins to CD4 site. • CD8 cells initially increase and may remain elevated. • As HIV infection progresses, CD4 T cells drop resulting in immunosuppression and susceptibility of patient to opportunistic infections. • Death comes due to immuno-incompetence.

34. ‘typical’ primary HIV-1 infection symptoms symptoms HIV proviral DNA HIV antibodies ‘window’ period HIV viral load HIV-1 p24 antigen 01 2 3 4 5 6 / 2 4 6 8 10 1° infection weeks years Time following infection

35. Laboratory Diagnosis of HIV Infection • Methods utilized to detect: • Antibody • Antigen • Viral nucleic acid • Virus in culture

36. ELISA Testing • First serological test developed to detect HIV infection. • Easy to perform. • Easily adapted to batch testing. • Highly sensitive and specific. • Antibodies detected in ELISA include those directed against: p24, gp120, gp160 and gp41, detected first in infection and appear in most individuals

37. ELISA Testing • ELISA tests useful for: • Screening blood products. • Diagnosing and monitoring patients. • Determining prevalence of infection. • Research investigations.

38. ELISA Testing • Different types of ELISA techniques used: • indirect • competitive • sandwich • ELISAs are for screening only, false positives do occur and may be due to AI disease, alcoholism, syphilis, and immunoproliferative diseases.

39. ELISA Sandwich

40. Other Screening Tests • Agglutination tests using latex particles, gelatin particles or microbeads are coated with HIV antigen and will agglutinate in the presence of antibody. • Dot-Blot Testing utilizes paper or nitrocellulose impregnated with antigen, patient serum is filtered through, and anti-antibody is added with enzyme label, color change is positive. • A rapid, cost-effective and may become an alternative to standard ELISA and Western blot testing.

42. Western Blot • Most popular confirmatory test. • Utilizes a lysate prepared from HIV virus. • The lysate is electrophoresed to separate out the HIV proteins (antigens). • The paper is cut into strips and reacted with test sera. • After incubation and washing anti-antibody tagged with radioisotope or enzyme is added. • Specific bands form where antibody has reacted with different antigens. • Most critical reagent of test is purest quality HIV antigen. • The following antigens must be present: p17, p24, p31, gp41, p51, p55, p66, gp120 and gp160.

43. Western Blot • Antibodies to p24 and p55 appear earliest but decrease or become undetectable. • Antibodies to gp31, gp41, gp 120, and gp160 appear later but are present throughout all stages of the disease.

44. Western Blot • Interpretation of results. • No bands, negative. • In order to be interpreted as positive a minimum of 3 bands directed against the following antigens must be present: p24, p31, gp41 or gp120/160. • CDC criteria require 2 bands of the following: p24, gp41 or gp120/160.

45. Spectrum of anti-HIV testing early recent / established advanced DNA PCR RNA PCR p24 Ag 3rd gen ELISA 1st gen ELISA Detuned ELISA 1wk 2wk 3wk 2mo 6mo 1yr 2yr 3yr +8yr

46. Western Blot • Expensive – $ 80 - 100 • technically more difficult • visual interpretation • lack standardisation • - performance • - interpretation • - indeterminate reactions – resolution of ?? • ‘Gold Standard’ for confirmation

47. Western Blot • Indeterminate results are those samples that produce bands but not enough to be positive, may be due to the following: • prior blood transfusions, even with non-HIV-1 infected blood • prior or current infection with syphilis • prior or current infection with malaria • autoimmune diseases (e.g., diabetes, Grave’s disease, etc) • infection with other human retroviruses • second or subsequent pregnancies in women. • run an alternate HIV confirmatory assay. • Quality control of Western Blot is critical and requires testing with strongly positive, weakly positive and negative controls.

48. Indirect immunofluorescence • Can be used to detect both virus and antibody to it. • Antibody detected by testing patient serum against antigen applied to a slide, incubated, washed and a fluorescent antibody added. • Virus is detected by fixing patient cells to slide, incubating with antibody.

50. Detection of p24 HIV antigen • The p24-antigen screening assay is an EIA performed on serum or plasma. • P24 antigen only present for short time, disappears when antibody to p24 appears. • Anti-HIV-1 bound to membrane, incubated with patient serum, second anti-HIV-1 antibody attached to enzyme label is added (sandwich technique), color change occurs. • Optical density measured, standard curve prepared to quantitate results.