In immunology two types of immune response are described depending on whether there is prior contact with the antigen.
• At this first contact, only lymphocytes with receptors specific to the antigen in question are stimulated and lead to the production of antibodies capable of neutralizing it. The lymphocytes capable of recognizing a specific antigen are very few and the production of antibodies - of low intensity and limited duration - is detectable only after a period of latency of several days. This is called the primary response. The specificity of the resulting seropositivity, however, makes it possible to detect contamination (seroconversion).
• Upon re-contact with an antigen that has already triggered a primary response, specific antibody production is found to increase rapidly after a short latency period. The secretion of IgG then reaches levels much higher than those observed during the primary response, while that of IgM is of the same order. This early and intense response, called secondary response, most often results in the destruction of infectious agents before any clinical sign.
• Many centuries before the discovery of microbes, it was noted that people who developed a contagious disease without death were then specifically immunized against the disease, without being protected against others.
• The ability to react appropriately to an already received stimulus supposes the existence of a memory. The immune memory is based on the existence of memory B and T lymphocytes, resulting from the clonal expansion due to the first contact with the antigen. Their lifespan is significantly higher than that of other lymphocytes and their high reactivity gives its rapid and intense character to the secondary response.
<span>Down syndrome
is a chromosomal condition that is associated with intellectual
disability, a characteristic facial appearance, and weak muscle tone
(hypotonia) in infancy. All affected individuals experience cognitive
delays, but the intellectual disability is usually mild to moderate.</span>
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Explanation:
The third-quarter moon, also known as the last quarter moon, rises around midnight and sets around noon. Crescent Waning From our vantage point, the Moon is nearly back to the point in its orbit where its dayside directly faces the Sun, and all we see is a thin curve
When you look at a waxing crescent moon, you see a thin fraction of the moon's illuminated side and a larger fraction of the moon's night side, which is submerged in the moon's own shadow. Earthshine on a waxing crescent moon
The Decline The Gibbous phase occurs when the illuminated portion of the Moon decreases from 99.9 percent to 50.1 percent. It begins shortly after the Full Moon and continues until the Third Quarter Moon. Waning refers to the fact that it is shrinking and becoming smaller, whereas gibbous refers to the oval-to-round shape.
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