MOI与TCID50的关系
MOI与TCID50的关系
Q: The author infected cells with an M.O.I of 50. The virus I titrated is 5X10(7)p.f.u/ml. So how much virus should I dilute to get an M.O.I of 5?
A:An MOI of 50 means 50 active viral particles per cell. So, if you have 10(6) cells on a plate x MOI (50)= 5x10(7) p.f.u for that plate (which equals one ml of your virus stock).
The number of p.f.u./ml was then calculated as TCID50 /ml x0.69.
Converting TCID[50] to MOI
How do I convert TCID[50] to MOI?
The easiest way to convert TCID[50] to an MOI value is to do the following:
Convert the titer by TCID[50] to plaque forming units (PFU). To do this, multiply the titer by 0.7.
Since plaque forming units represents the estimated number of infectious units per volume of virus material, one can estimate the total number of infectous particles.
Next, divide the number of infectious particles by the number of cells to be infected to obtain the MOI. Then, dilute the virus accordingly in order to obtain 0.1 to 0.01 MOI.
For example,
If the TCID[50] titer for a given virus is 10(7.25) TCID[50] per 0.2 ml, 10(7.25) is approximately 17,782,794 (the inverse log of 7.25), and when multiplied by 0.7 gives 12,447,956 PFU per 0.2 ml. If you were going to infect 10 million cells at an MOI of 0.1, you need 1,000,000 infectious particles. For the above example, you should dilute 0.2 ml of the virus stock at least 1:12.5 to obtain 1,000,000 infectious particles per 0.2 ml, then this volume (0.2 ml x 12.5 = 2.5 ml) should be diluted appropriately to infect the number of vessels. (Usually we infect a 75 cm2 flask with 2 mL of diluted virus or a 150 cm2 flask with 5 mL of diluted virus).
What do MOI and PFU mean?
The term MOI stands for Multiplicity Of Infection. This value describes the ratio of the number of virions per target cell at the time the virus is added to the culture.
The term PFU stands for Plaque Forming Unit. One PFU/ml is defined as 1 lytic event (seen as a plaque on a lawn of 293 cells) per milliliter of media. This is a measure of viral titer.
Additional information can be found in the following reference: Nature
Medicine, vol. 3, number 7, July 1997. Sensitivity and Reproducibility in Adenoviral Infectious Titer Determination. Once the viral titer is determined, a given MOI can be specified and used for the target cells.
什么是MOI？
MOI 是multiplicity of infection的缩写，中文译为感染复数。传统的MOI 概念起源于噬菌体感染细菌的研究。其含义是感染时噬菌体与细菌的数量比值，也就是平均每个细菌感染噬菌体的数量。噬菌体的数量单位为pfu。一般认为MOI 是一个比值，没有单位，其实其隐含的单位是pfu number/cell。后来MOI被普遍用于病毒感染细胞的研究中，含义是感染时病毒与细胞数量的比值。
然而，由于病毒的数量单位有不同的表示方式，从而使MOI产生了不同的含义。能产生细胞裂解效应的病毒例如腺病毒、单纯疱疹病毒等习惯上仍用pfu表示病毒数量，因此其MOI的含义与传统的概念相同。而对于某些病毒如AAV病毒，无法用pfu表示病毒的数量，而是采用TU、IU、病毒颗粒（viral particles, v.p）或基因组数量（vector genome,v.g.）来表示病毒数量，因此其MOI就有了不同含义。采用TU或IU，MOI的含义便是TU number/cell 或IU number/cell。采用v.p.，MOI的含义便是v.p. number/cell 。采用v.g，MOI的含义便是v.g. number/cell。
可以将上述不同的MOI 表示方式分为2种：
1）以活性单位表示病毒数量，如pfu, TU, IU。这时MOI的含义是指平均每个细胞感染病毒的活性单位数。
2）以病毒颗粒或基因组数表示病毒数量，如v.p. 或v.g. 。这时MOI的含义是指平均每个细胞感染病毒的病毒颗粒或基因组数。
值得一提的是，上述2种不同的MOI 表示方式在含义和数值上都有所不同。前一种是传统意义上的MOI，后一种MOI表示方式的含义更为简化和直观，也逐步被一些研究者采用。
传统意义上的MOI的测定，其原理是基于病毒感染细胞是一种随机事件，遵循Poisson分布规律，可计算出感染一定比例的培养细胞所需的感染复数（MOI）。其公式为：
P(k) = 1- P(0) ,P(0) = e-m 或m = -InP（0）。
其中：
P(k) 为被感染细胞的百分率
P(0)为未被感染细胞的百分率
m为MOI值
例如，如果要感染培养皿中99%的培养细胞，则：
P(0) = 1% = 0.01
m = -In(0.01)= 4.6 pfu/cell。
由此可以看出，由于病毒特性和研究者习惯的不同，MOI的单位由原来约定俗成的pfu number/cell变成多种表示单位。在阅读文献和写作论文时，应注意MOI 的具体含义和单位。
PFU: plaque forming units A measure of the biological activity of a virus sample.
MOI: multiplicity of infection MOI= #PFU/cell eg. If 1X106 cells are infected with 5X106 PFU, the MOI is calculated as 5X106/1X106=5 CPE: cytopathic effect
The Poisson distribution is used to calculate the proportion (P) of cells infected with K (0, 1, 2, 3, etc.) PFU when virus is added to cells at a particular MOI (m).
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PFU：病毒样本生物活性的测量
MOI：=#PFU/cell 如果用5*106的PFU感染1*106细胞，则MOI=5*106/1*106=5
Sample problem:
You infect a monolayer of 1X107 cells with 0.1 ml. of a sample of virus the titer of which is 1X 109 PFU/ml.
What is the MOI of this infection, and how many cells are infected?
0.1ml. ( 1 X 109 PFU/ml ) = 1 X 108 PFU
MOI = PFU/cell =1 X 108 / 1 X 107 =10
The proportion of infected cells = 1- the proportion of uninfected cells = 1-e-m =1-e-10 =0.999952
The number of infected cells = the total number of cells multiplied by the proportion of infected cells = (1X107) (0.999952) = 0.999952X107. Thus at an MOI of 10, most cells are infected.
Now you calculate the number of cells that are uninfected, infected with one PFU, and multiply infected.
你用0.1ml滴度为1*109的病毒样本感染一个1*107单层平铺的细胞，
这次感染的MOI是多少？有多少细胞被感染？
0.1ml(1X109PFU/ml)=1X108PFU
MOI=PFU/cell=1X108/1X107 =10
感染细胞的比例=1-未被感染的细胞=1-e-m=1-e-10=0.999952
感染细胞的数目=细胞总数X被感染细胞的比例=（1X107）（0.999952）
因此在10MOI时更多的细胞被感染