immunitiy to HIV Flashcards
What are the predominant routes of HIV infection, and how does perinatal infection occur?
The predominant routes of HIV infection are through mucosal surfaces, including the male and female genital tracts, rectal surfaces, and gut surfaces. Perinatal infection occurs when the virus is transmitted from mother to child during childbirth, breastfeeding, or pregnancy.
Explain Fiebig staging and its purpose in HIV infection diagnosis.
Fiebig staging is a 6-stage classification system used to stage early HIV infection based on the emergence of viral markers and host antibody responses. It helps identify different stages of infection before and after seroconversion. The system is named after its first author and provides insights into the progression of the disease.
What is the significance of the acute stage of HIV infection (Fiebig I/II)?
The acute stage of HIV infection (Fiebig I/II) occurs prior to seroconversion and is characterized by peak viremia. It’s associated with a cytokine storm, where proinflammatory cytokine levels are high, leading to symptoms like fever, pharyngitis, and lymphadenopathy. During this stage, the ELISA test detects anti-p24 antibodies, and viral proteins can be detected in western blots.
Describe the concept of the viral set point in HIV infection.
The viral set point is a point established around 3-6 months after initial HIV infection where the level of viral replication in the host remains relatively constant. It represents an equilibrium between host immunity to HIV and the rate of viral turnover. A higher viral load in the blood plasma is associated with faster disease progression, while a lower viral load leads to slower disease progression.
How does the immune response to HIV infection unfold?
The immune response to HIV infection involves several stages: dissemination of the virus to lymphoid tissues, acute phase with rapid viraemia increase, decline in viral load to a set point, decline in CD4+ T cells, emergence of HIV-specific CD8+ cytotoxic T cell responses, appearance of HIV-specific binding antibodies, decline in CD4+ T cells during chronic infection, emergence of neutralizing antibodies, and immune evasion leading to opportunistic infections and AIDS.
Explain the role of Langerhans’ cells in HIV transmission.
Langerhans’ cells are dendritic cells found in genital epithelium that interact with HIV during heterosexual contact. They express CD207 (langerin) that captures virus by binding to gp120, leading to internalization and degradation of virus particles. Activated Langerhans’ cells migrate to draining lymph nodes for antigen presentation to CD4+ and CD8+ T cells, and can also become infected by HIV.
How does the process of HIV dissemination occur?
After transmission, HIV disseminates to lymphoid tissues. Infected CD4+ T cells migrate to mucosal tissues, leading to increased viral replication in lymph organs and high viral loads in peripheral blood. There’s also a rapid depletion of CD4+ T cells, particularly in gut lymphoid tissues. Tissue macrophages and dendritic cells can become infected, contributing to viral dissemination.
How does the immune response attempt to control viremia during HIV infection?
Tissue dendritic cells present viral peptides to CD8+ and CD4+ T cells in lymph nodes. HIV-specific CD8+ cytotoxic T cells target and kill infected cells, reducing viral replication and allowing CD4+ T helper lymphocyte numbers to increase. This response helps control viral load, but the virus is not eradicated completely.
Describe the process of seroconversion in HIV infection.
Seroconversion refers to the appearance of antibodies against HIV in peripheral blood. It occurs around 4-6 weeks after transmission, sometimes taking up to 3 months. For HIV-specific antibodies to be generated, viral particles and proteins must be captured by follicular dendritic cells in lymphoid follicles. HIV-specific CD4+ helper T cells provide activation signals for B cells to differentiate into plasma cells, leading to antibody production
What is the primary role of Langerhans’ cells in HIV transmission?
A) They produce proinflammatory cytokines.
B) They directly attack and destroy HIV particles.
C) They migrate to lymph nodes and present antigens.
D) They mediate the production of neutralizing antibodies.
C) They migrate to lymph nodes and present antigens.
What characterizes the viral set point in HIV infection?
A) The time of initial infection with HIV.
B) The stage where fever and pharyngitis occur.
C) The equilibrium between host immunity and viral replication.
D) The period when neutralizing antibodies emerge.
C) The equilibrium between host immunity and viral replication.
