IMMUNOLOGY TEXTBOOK - Mercury Podillia 2013

ACQUIRED IMMUNODEFICIENCY STATES

The ability of the body's immune system to resist various infectious agents (Bacteria, Viruses, Fungi) is an essential component of human survival. This capacity relies on two mechanisms: non-specific anti-infective resistance, which targets a broad range of pathogens, and The Development of specific acquired Immunity against particular microorganisms.

Population-level acquired resistance develops through adaptive immunity in the majority of individuals following vaccination or infection. Susceptibility to any infection is individual and always stems from immune deficiency. When resistance—or immunity—is present, even highly dangerous infections fail to take hold.

Opportunistic bacteria and fungi can induce an infection in a body with fully functioning defense mechanisms only when The ratio of the infectious dose to a single defense factor (such as a phagocyte) exceeds a critical threshold, representing a state of relative immunodeficiency. In such cases, the phagocyte is unable to engulf and destroy the given number of microbes. Typically, Infections caused by opportunistic pathogens occur in individuals with compromised immune systems, where even a small dose of microorganisms—insufficient to infect healthy individuals—is enough to trigger disease, indicating an absolute immunodeficiency.

Consequently, identifying the causes of weakened immune defense, characterizing conditions accompanied by impaired immune responses, and developing Methods for immune correction are crucial objectives in the Diagnosis and Treatment of acquired immunodeficiency states.

Immune Deficiency and Infections

Infection (infectious process) is a pathological condition resulting from the interaction between a pathogenic microorganism and the Cells and Tissues of a non-immune, susceptible host. It is characterized by microbial Replication, alterations in host reactivity, and tissue damage. Infection represents only one possible outcome of the host-pathogen interaction. Another—and likely more frequent—outcome is natural resistance, the establishment of immunity, or its enhancement (if already present).

Three core conditions are necessary for an infectious process to occur: a pathogenic agent, its penetration into the internal environment of the host, and host susceptibility. The progression of the infection depends on the extent to which these three conditions are met. The first condition relies on the dose and virulence of the pathogen; the second, on the integrity of the host's natural barriers and the site of entry; and the third, on the host's immune resistance.

Although the initiation and intensity of an infection depend on the dose, virulence, and route of entry, the primary determinant remains the degree of deficiency in the host's innate or acquired immunity. Ultimately, immune deficiency—whether relative (to a specific pathogen) or absolute—serves as the decisive factor in the development of an infection.

Therefore, an infectious disease is, above all, an immunodeficiency disorder in an individual where the pathogenicity of the invading agent exceeds their "immune capacity" at the time of exposure.

The Human Body's ability to resist various microorganisms is driven by two mechanisms: non-specific anti-infective resistance, which immediately targets a multitude of infectious agents, and the development of specific acquired immunity tailored to particular microorganisms.

Acquired population resistance arises through adaptive immunity in the majority of the population following vaccination or prior infection. Susceptibility to all infections is individual and invariably stems from a lack of immunity to the specific infection. Where resistance—immunity—exists, even particularly dangerous infections do not develop. The elimination of smallpox was achieved through the eradication of susceptible individuals via universal vaccination. If similarly highly effective Vaccines were available, all other infections could be minimized, leaving only immunocompromised individuals vulnerable to illness.

Opportunistic bacteria and fungi trigger an infectious process in an Organism with normal defense mechanisms only when the ratio of the infectious dose per unit of defense factor (e.g., a single phagocyte) exceeds a critical threshold, which constitutes relative immunodeficiency. In this scenario, the phagocyte cannot engulf and digest the given microbial load. Typically, infections driven by opportunistic microbes manifest in individuals with compromised immune systems, where a low dose of microorganisms—harmless to individuals with a normal immune system—is sufficient to cause disease, thereby indicating absolute immunodeficiency.

Obligate pathogens (such as those causing exceptionally dangerous infections like plague, anthrax, etc.) possess high virulence and mechanisms to neutralize and overcome the natural immune barriers of a normal, yet non-immune, organism (relative immunodeficiency). Protection against them requires prior activation of The Immune System, the induction of Antibodies and/or immune T cells—in other words, the establishment of immunity—to prevent these bacteria from overpowering the host.

Many viruses are capable of breaching the barriers of natural innate immunity; however, once acquired immunity is induced via vaccination (e.g., measles, poliomyelitis, Influenza, etc.), the infection is successfully prevented.