Saturday, July 16, 2005

Zinkernagel Speaks, I Remain Silent

Yesterday, I heard Rolf Zinkernagel speak on immunological memory in his lecture:

"On Anti-Viral Immunity and Vaccines," Hyundai-Kia Nobel Laureate Lecture Series V, July 15, 2005, Inchon Memorial Hall, Korea University.

As it turns out, he's skeptical about the analytical and practical usefulness of the expression "immunological memory," though at a very general level, he accepts the expression, for he presupposes its meaning in his lecture:

"Immunological memory describes the fact that humans infected once with measles-, pox-, or polio viruses are subsequently resistant against disease caused by re-infections" (13a).

At this general level, the 'memory' is nothing but another word for "resistance," and since the people in the field do use the expression, Zinkernagel does as well.

However, he notes the possibility that the expression "immunological memory" implies something that might not really exist, the creation of a "memory" of a disease in the immune system that enables it to "recall" an infecting agent and fight against it. Why might it not exist? Because:

"[I]f a naive host survives a first infection, this host basically does not need immunological memory to survive the second infection. Vice versa, if a host does not survive the first infection, he certainly does not need immunological memory thereafter" (13a).

Even assuming that there is such a thing as immunological memory, Zinkernagel notes that the expression is used in two very different ways, to identify:

1. "a special quality of T or B cells that have acquired a new status of 'memory' when compared to naive cells or effector cells" (11b),


2. "a low-level antigen-driven response, consequently protection immunological memory eventually disappears without antigen" (12a).

Given this ambiguity in the meaning of the expression, much work remains to be done in order to clarify precisely what is going on in our immune systems that allows us to survive re-infections.

I won't attempt to say more than that since the lecture was extremely technical, and I'm too ignorant of this field to speak without saying something foolish.

I would, however, like to focus on an offhand remark made by Zinkernagel. He noted in passing that from the perspective of evolutionary biology, we need not live past 25 since by that time we will have reproduced and thus have no further benefit to the species, so our extra 50 years are merely a "luxury."

Now, I assume that he was using a bit of deflating irony in this remark, perhaps to remind us that the evolutionary process doesn't care for us as individuals, but he also seemed to assume the correctness of this view -- as a piece of biological wisdom.

I think that it's wrong.

It seems implausible to me that a 'luxury' of 50 extra years would be endowed on a species if these extra years had no survival benefit in terms of an evolutionary process. I would argue that the extra 50 years enable our species to embody an enormous "cultural memory" that greatly enhances our fitness in the struggle for survival and that this cultural memory can only be effectively passed on from generation to generation because of our 'luxury' of having so many extra years.

And I would have made this point, too, except that after I had raised my hand toward the end of the question period, the dean announed that given the shortness of time, the remaining questions should be posed by persons working on research in the field of immunology.

Excluded from the ranks of those qualified to speak, I held my tongue.


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