Which of the following statements is most correct regarding Leishmania?

Correct Answer: D

Rationale: The correct answer is D because visceral leishmaniasis is indeed the most severe form of leishmaniasis. Visceral leishmaniasis affects internal organs and can be fatal if left untreated. A is incorrect because Leishmania is a protozoan parasite, not a bacterium. B is incorrect because leishmaniasis can affect individuals with normal immune systems, not just those with severe immunodeficiency. C is incorrect because a TH1 response is actually protective against severe leishmaniasis, not a TH2 response.

Correct Answer: A

Rationale: The correct answer is A because T cells do not recognize three-dimensional structures of a pathogen. T cell receptors interact with processed antigen fragments presented by MHC molecules on antigen-presenting cells. Choice B is correct because T cell receptors possess specificity for antigens. Choice C is incorrect because T cell receptors have multiple antigen-binding sites. Choice D is incorrect as T cell receptors can be secreted as soluble forms.

Correct Answer: D

Rationale: The correct answer is D: Artificial passive. Plasma therapy involves administering preformed antibodies to provide immediate protection against a specific pathogen. This is considered artificial passive immunity because the antibodies are obtained from an external source rather than being produced by the individual's immune system. Explanation: 1. Natural active immunity (Choice A) is when the body produces its antibodies after exposure to a pathogen, which is not the case in plasma therapy. 2. Natural passive immunity (Choice B) is when antibodies are passed from mother to fetus or through breast milk, not obtained through plasma therapy. 3. Artificial active immunity (Choice C) involves vaccination to stimulate the body's immune response, which is different from plasma therapy. In summary, the correct answer is D (Artificial passive) because plasma therapy provides immediate immunity through externally sourced antibodies, distinguishing it from the other types of immunological protection.

Correct Answer: C

Rationale: The correct answer is C: 1-b, 2-d, 3-a, 4-c. 1. The first match should be b, as it aligns with the order given. 2. The second match should be d, as it aligns with the order given. 3. The third match should be a, as it aligns with the order given. 4. The fourth match should be c, as it aligns with the order given. Therefore, option C is the correct match based on the given order. Other choices are incorrect because they do not align with the given order of matches.

Correct Answer: B

Rationale: The correct answer is B: Passive natural immunity occurs. This type of immunity is achieved through the transfer of antibodies (IgG) from the mother to the fetus during pregnancy. The antibodies provide protection to the newborn for the first few months of life. It is considered passive because the newborn is not actively producing the antibodies themselves. A: Active natural immunity occurs when the body produces its antibodies in response to exposure to an antigen. This is not the case for newborns receiving maternal IgG. C: Active artificial immunity occurs when the body is intentionally exposed to an antigen, such as through vaccination, to stimulate an immune response. This is not relevant to the scenario described. D: Passive artificial immunity occurs when pre-formed antibodies are transferred to an individual through a medical intervention, such as receiving immune globulin. This is not applicable to the situation of maternal transmission of IgG to newborns.